The Collaborative International Dictionary of English v.0.48:

Liliaceous \Lil`i*a"ceous\ (l[i^]l`[i^]*[=a]"sh[u^]s), a. [L.
   liliaceus, fr. lilium lily. See Lily.] (Bot.)
   (a) Of or pertaining to a natural order of which the lily,
       tulip, and hyacinth are well-known examples.
   (b) Like the blossom of a lily in general form.
       [1913 Webster]

WordNet (r) 3.0 (2006):

liliaceous
    adj 1: of or pertaining to or characteristic of plants of the
           family Liliaceae