Wordnet 3.0
NOUN (1)
1. 
 thinking again about a choice previously made; 
- Example: "he had second thoughts about his purchase"[syn: reconsideration, second thought, afterthought, rethink]
VERB (1)
1.  change one's mind; 
- Example: "He rethought his decision to take a vacation"
WordNet (r) 3.0 (2006):
rethink
    n 1: thinking again about a choice previously made; "he had
         second thoughts about his purchase" [syn:
         reconsideration, second thought, afterthought,
         rethink]
    v 1: change one's mind; "He rethought his decision to take a
         vacation"