Wordnet 3.0
VERB (2)
1. 
 take watchful responsibility for; 
- Example: "I baby-sit the neighbor's plants when she is out of town"2. 
 work or act as a baby-sitter; 
- Example: "I cannot baby-sit tonight I have too much homework to do"; 
[syn: baby-sit, sit]
The Collaborative International Dictionary of English v.0.48:
baby-sit \baby-sit\ v.
   act as a baby-sitter
   Syn: babysit, sit
        [WordNet 1.5] babysitter
WordNet (r) 3.0 (2006):
baby-sit
    v 1: take watchful responsibility for; "I baby-sit the
         neighbor's plants when she is out of town"
    2: work or act as a baby-sitter; "I cannot baby-sit tonight; I
       have too much homework to do" [syn: baby-sit, sit]