The Collaborative International Dictionary of English v.0.48:

Acolyte \Ac`o*lyte\, n. [LL. acolythus, acoluthus, Gr. ?
   following, attending: cf. F. acolyte.]
   [1913 Webster]
   1. (Eccl.) One who has received the highest of the four minor
      orders in the Catholic church, being ordained to carry the
      wine and water and the lights at the Mass.
      [1913 Webster]

   2. One who attends; an assistant. "With such chiefs, and with
      James and John as acolytes." --Motley.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

altar boy \al"tar boy\, n.
   a boy who assists a priest at the clebration of the Holy Mass
   and other forms of public worship; -- also called acolyte.
   [PJC]

WordNet (r) 3.0 (2006):

acolyte
    n 1: someone who assists a priest or minister in a liturgical
         service; a cleric ordained in the highest of the minor
         orders in the Roman Catholic Church but not in the Anglican
         Church or the Eastern Orthodox Churches