Wordnet 3.0
VERB (3)
1. 
 make sparse; 
- Example: "thin out the young plants"2. 
 become sparser; 
- Example: "Towards the end of town, the houses thinned out"3. 
 lessen the strength or flavor of a solution or mixture; 
- Example: "cut bourbon"[syn: dilute, thin, thin out, reduce, cut]
WordNet (r) 3.0 (2006):
thin out
    v 1: make sparse; "thin out the young plants"
    2: become sparser; "Towards the end of town, the houses thinned
       out"
    3: lessen the strength or flavor of a solution or mixture; "cut
       bourbon" [syn: dilute, thin, thin out, reduce, cut]