The Collaborative International Dictionary of English v.0.48:

capitation \cap`i*ta"tion\ (k[a^]p`[i^]*t[=a]"sh[u^]n), n. [L.
   capitatio a poll tax, fr. caput head; cf. F. capitation.]
   1. A numbering of heads or individuals. [Obs.] --Sir T.
      Browne.
      [1913 Webster]

   2. A tax upon each head or person, without reference to
      property; a poll tax.
      [1913 Webster]

WordNet (r) 3.0 (2006):

capitation
    n 1: a tax levied on the basis of a fixed amount per person

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

CAPITATION. A poll tax; an imposition which is yearly laid on each person
according to his estate and ability.
     2. The Constitution of the United States provides that "no capitation,
or other direct tax, shall be laid, unless in proportion to the census, or
enumeration, therein before directed to be taken." Art. 1, s. 9, n. 4. See 3
Dall. 171; 5 Wheat. 317.