Employ specialist? No pressure (5)
I believe the answer is:
exert
'employ' is the definition.
(eg exerting strength is using or employing it)
'specialist? no pressure' is the wordplay.
'specialist?' becomes 'expert' (a specialist is an expert in a field).
'no' suggests deleting specific letters.
'pressure' becomes 'p' (scientific abbreviation).
'expert' with 'p' taken away is 'EXERT'.
(Other definitions for exert that I've seen before include "Act upon" , "Expend" , "Make a great effort" , "Work strenuously" , "Bring into use, apply" .)