WordWeb Online

1. Define clearly
   "I cannot pin down the rules for this game";
   - peg down [informal], nail down, narrow down, narrow, specify
    
2. Place in a confining or embarrassing position
   "He was pinned down in a difficult situation";
   - trap
    
3. Attach with or as if with a pin
   "pin down a picture";
   - pin up

Derived forms: pins down, pinning down, pinned down

Type of: attach, confine, detain, determine