The Collaborative International Dictionary of English v.0.48:

Rosaceous \Ro*sa"ceous\, a. [L. rosaceus, fr. rosa rose.]
   1. (Bot.)
      (a) Of or pertaining to a natural order of plants
          (Rosaceae) of which the rose is the type. It
          includes also the plums and cherries, meadowsweet,
          brambles, the strawberry, the hawthorn, applies,
          pears, service trees, and quinces.
      (b) Like a rose in shape or appearance; as, a rosaceous
          corolla.
          [1913 Webster]

   2. Of a pure purpish pink color.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rosaceous
    adj 1: of or pertaining to or characteristic of plants of the
           family Rosaceae
    2: of something having a dusty purplish pink color; "the roseate
       glow of dawn" [syn: rose, roseate, rosaceous]