The Collaborative International Dictionary of English v.0.48:

Deaconess \Dea"con*ess\, n. (Eccl.)
   A female deacon; as:
   (a) (Primitive Ch.) One of an order of women whose duties
       resembled those of deacons.
   (b) (Ch. of Eng. and Prot. Epis. Ch.) A woman set apart for
       church work by a bishop.
   (c) A woman chosen as a helper in church work, as among the
       Congregationalists.
       [1913 Webster]

WordNet (r) 3.0 (2006):

deaconess
    n 1: a woman deacon

Easton's 1897 Bible Dictionary:

Deaconess
   Rom. 16:1, 3, 12; Phil. 4:2, 3; 1 Tim. 3:11; 5:9, 10; Titus 2:3,
   4). In these passages it is evident that females were then
   engaged in various Christian ministrations. Pliny makes mention
   of them also in his letter to Trajan (A.D. 110).