Style of a pain put under pressure (7)
I believe the answer is:
panache
'style' is the definition.
(panache means style or verve)
'a pain put under pressure' is the wordplay.
'a' becomes 'an'.
'pain' becomes 'ache' (ache is a kind of pain).
'put under' says to put letters next to each other.
'pressure' becomes 'p' (scientific abbreviation).
'an'+'ache'='anache'
'anache' put after 'p' is 'PANACHE'.
'of' acts as a link.
(Other definitions for panache that I've seen before include "Flamboyant confidence" , "A dashing manner" , "Dash and verve" , "flourish" , "Swagger, grand manner" .)