Show nurses fine needle (7)
I believe the answer is:
provoke
'needle' is the definition.
(I know that needle is a kind of provoke)
'show nurses fine' is the wordplay.
'show' becomes 'prove' (proving is a kind of showing).
'nurses' means one lot of letters goes inside another (nurse can mean to hold onto or harbour).
'fine' becomes 'ok' (synonyms).
'prove' placed around 'ok' is 'PROVOKE'.
(Other definitions for provoke that I've seen before include "Irritate - arouse" , "needle" , "Make angry or incite to action" , "Deliberately annoy" , "Goad" .)