Get rid of undesirable impulse under pressure (5)
I believe the answer is:
purge
'get rid of' is the definition.
(I've seen this before)
'undesirable impulse under pressure' is the wordplay.
'undesirable impulse' becomes 'urge' (synonyms. I am not sure about the 'undesirable' bit.).
'under' says to put letters next to each other (below, in a down clue).
'pressure' becomes 'p' (abbreviation).
'urge' put after 'p' is 'PURGE'.
Can you help me to learn more?
(Other definitions for purge that I've seen before include "Elimination of "undesirables"" , "Remove impurities from" , "Cleanse of unwanted elements" , "Remove by cleansing" , "Purify, clear out" .)