The Collaborative International Dictionary of English v.0.48:

Acinus \Ac"i*nus\ ([a^]s"[i^]*n[u^]s), n.; pl. Acini. [L.,
   grape, grapestone.]
   1. (Bot.)
      (a) One of the small grains or drupelets which make up
          some kinds of fruit, as the blackberry, raspberry,
          etc.
      (b) A grapestone.
          [1913 Webster]

   2. (Anat.) One of the granular masses which constitute a
      racemose or compound gland, as the pancreas; also, one of
      the saccular recesses in the lobules of a racemose gland.
      --Quain.
      [1913 Webster]

WordNet (r) 3.0 (2006):

acinus
    n 1: one of the small drupes making up an aggregate or multiple
         fruit like a blackberry
    2: one of the small sacs or saclike dilations in a compound
       gland