extern
Concise Oxford English Dictionary © 2008 Oxford University Press:
extern /ɪkˈstəːn, ɛk-/
▶noun
- 1 US a non-resident doctor or other worker in a hospital.
- 2 (in a strictly enclosed order of nuns) a sister who does not live exclusively within the enclosure and goes on outside errands.
– origin C16 (as an adj. in the sense ‘external’): from Fr. externe or L. externus, from exter ‘outer’.
'extern' also found in these Oxford entries:

