Wordnet 3.0
ADJECTIVE (2)
1. 
 of or pertaining to the botanical genus Allium; 
- Example: "onions, leeks, garlic, chives are alliaceous plants"2. 
 smelling of onions or garlic; 
The Collaborative International Dictionary of English v.0.48:
Alliaceous \Al`li*a"ceous\, a.
   Of or pertaining to the genus Allium, or garlic, onions,
   leeks, etc.; having the smell or taste of garlic or onions.
   [1913 Webster]
WordNet (r) 3.0 (2006):
alliaceous
    adj 1: of or pertaining to the botanical genus Allium; "onions,
           leeks, garlic, chives are alliaceous plants"
    2: smelling of onions or garlic