Stop, being about to relax (5)
I believe the answer is:
cease
'stop' is the definition.
(synonyms)
'about to relax' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to relax' becomes 'ease' (eg to ease a restriction is to relax it).
'c'+'ease'='CEASE'
'being' is the link.
(Other definitions for cease that I've seen before include "Discontinue" , "Stop, finish" , "Stop, terminate" , "Desist" , "Stop, give over" .)