Puritan outfit under pressure (4)
I believe the answer is:
prig
'puritan' is the definition.
(I've seen this before)
'outfit under pressure' is the wordplay.
'outfit' becomes 'rig' (rigging is a kind of outfiting).
'under' means one lot of letters go next to another.
'pressure' becomes 'p' (abbreviation).
'rig' after 'p' is 'PRIG'.
(Other definitions for prig that I've seen before include "Stuck-up person" , "Snooty type?" , "Smugly self-righteous person" , "Self-righteous moralist" , "Excessively moralistic person" .)