reentrant

Short definition from Wiktionary

Adjective

1. 1
   Reentering; pointing inward.
2. 2
   Such that the corresponding lock can be reacquired by the locking thread.
3. 3
   That may be executed more than once at a time either by different threads, or because of recursion.
4. 4
   Designed to return to the Earth's atmosphere.
5. 5
   Of or pertaining to reentry (in the heart).
6. 6
   Having the strings not ordered according to pitch (having a re-entry).

Noun

1. 1
   An angle or part that reenters itself.
2. 2
   One who enters (the labour market, etc.) again.
3. 3
   A valley between a pair of parallel ridges.