The Collaborative International Dictionary of English v.0.48:

Administrator \Ad*min`is*tra"tor\, n. [L.]
   1. One who administers affairs; one who directs, manages,
      executes, or dispenses, whether in civil, judicial,
      political, or ecclesiastical affairs; a manager.
      [1913 Webster]

   2. (Law) A man who manages or settles the estate of an
      intestate, or of a testator when there is no competent
      executor; one to whom the right of administration has been
      committed by competent authority.
      [1913 Webster]

WordNet (r) 3.0 (2006):

administrator
    n 1: someone who administers a business [syn: administrator,
         decision maker]
    2: the party appointed by a probate court to distribute the
       estate of someone who dies without a will or without naming
       an executor
    3: someone who manages a government agency or department [syn:
       administrator, executive]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "administrator":
   academic dean, administration, agent, chancellor, conductor, dean,
   dean of men, dean of women, deputy, directeur, director, exec,
   governor, headmaster, headmistress, impresario, intendant, manager,
   master, officer, official, president, principal, producer, provost,
   rector, responsible person, supercargo, vice-chancellor



Bouvier's Law Dictionary, Revised 6th Ed (1856):

ADMINISTRATOR, trusts. An administrator is a person lawfully appointed,
with his assent, by an officer having jurisdiction, to manage and settle the
estate of a deceased person who has left no executor, or one who is for the
time incompetent or unable to act.
     2. It will be proper to consider, first, his rights; secondly, his
duties.; thirdly, the number of administrators, and their joint and several
powers; fourthly, the several kinds of administrators.
     3.-1. By the grant of the letters, of administration, the
administrator is vested with full and ample power, unless restrained to some
special administration, to take possession of all the personal estate of the
deceased and to sell it; to collect the debts due to him; and to represent
him in all matters which relate to his chattels real or personal.  He is
authorized to pay the debts of the, intestate in the order dire ted by law;
and, in the United States, he is generally entitled to a just compensation,
which is allowed him as commissions on the amount which passes through his
hands.
     4.-2. He is bound to use due diligence in the management of the
estate; and he is generally on his appointment required to give security
that he will do so; he is responsible for any waste which. may happen for
his default. See Devastavit.
     5. Administrators are authorized to bring and defend actions. They sue
and are sued in their own names; as, A B, administrator of C D, v. E F; or E
F v. A B, administrator of C D.
     6.-3. As to the number of administrators. There may be one or more.
When there are several they must, in general, act together in bringing
suits, and they must all be sued ; but, like executors, the acts of each,
which relate to the delivery, gift, sale, payment, possession. or release of
the intestate's goods, are considered as of equal validity as the acts of
all, for they have a joint power and authority over the whole. Bac. Ab.
Executor, C 4; 11 Vin. Ab. 358; Com. Dig. Administration, B 12; 1 Dane's Ab.
383; 2 Litt. R. 315. On the death of one of several joint administrators,
the whole authority is vested in the survivors.
     7.-4. Administrators are general, or those who have right to
administer the whole estate of the intestate; or special, that is, those who
administer it in part, or for a limited time.
     8.-1. General administrators are of two kinds, namely: first, when
the grant of administration is unlimited, and the administrator is required
to administer the whole estate, under the intestate laws, secondly, when the
grant is made with the annexation of the will, which is the guide to the
administrator to administer and distribute the estate.  This latter
administration is granted when the deceased has made a will, and either he
has not appointed an executor, or having appointed one he refuses to serve,
or dies, or is incompetent to act; this last kind is called an administrator
cum testamento annexo. 1 Will. on Wills, 309.
     9.-2. Special administrators are of two kinds; first, when the
administration is limited to part of the estate, as for example, when the
former administrator has died, leaving a part of the estate unadministered,
an administrator is appointed to administer the remainder, and he is called
an administrator de bonis non. He has all the powers of a common
administrator. Bac. Ab. Executors, B 1; Sw. 396; Roll. Ab. 907; 6 Sm. &
Marsh. 323. When an executor dies leaving a part of the estate
unadministered, the administrator appointed to complete the execution of the
win is called an administrator de bonis non, cum testamento annexo. Com.
Dig. Administrator, B 1. Secondly, When the authority of the administrator
is limited as to time. Administrators of this kind are, 1. An administrator
durante minore oetate. This administrator is appointed to act as such during
the minority of an infant executor, until the latter shall, attain his
lawful age to act. Godolph. 102; 5 Co. 29. His powers extend to administer
the estate so far as to collect the same, sell a sufficiency of the personal
property to pay the debts, sell bona peritura, and perform such other acts
as require immediate attention. He may sue and be sued. Bac. Ab. Executor, B
1 ; Roll. Ab. 110; Cro. Eliz. 718.  The powers of such an administrator
cease, as soon as the infant executor attains the age at which the law
authorizes him to act for himself, which, at common law, is seventeen years,
but by statutory provision in several states twenty-one years.
    10.-2. An administrator durante absentia, is one who is appointed to
administer the estate during the absence of the executor, before he has
proved the will.  The powers of this administrator continue until the return
of the executor, and. then his powers cease upon the probate of the will by
the executor. 4 Hagg. 860. In England it has been holden, that the death of
the executor abroad does not determine the authority of the administrator
durante absentia. 3 Bos. & Pull. 26.
    11.-3. An administrator pendente lite. Administration pendente lite
may be granted pending the controversy respecting an alleged will and it has
been granted pending a contest as to, the right to administration. 2 P. Wms.
589; 2 Atk. 286; 2 Cas. temp. Lee, 258. The administrator pendente lite is
merely an officer of the court, and holds the property only till the suit
terminates. 1 Hagg. 313. He may maintain suits, 1 Ves. sen. 325; 2 Ves. & B.
97; 1 Ball & B. 192; though his power does not extend to the distribution of
the assets. 1 Ball & B. 192.