Openings for staff, promising, at health centre (3)
I believe the answer is:
spa
'health centre' is the definition.
(I've seen this before)
'openings for staff promising at' is the wordplay.
'openings for' suggests taking the first letters (I've seen 'opening for' mean this).
The first letters of 'staff promising at' is 'SPA'.
(Other definitions for spa that I've seen before include "Where people go for spring" , "Cheltenham or Bath?" , "eg Bath" , "Bath - mineral water spring" , "E.g. Harrogate" .)