Cabbie's first comfort stop (5)
I believe the answer is:
cease
'stop' is the definition.
(synonyms)
'cabbie's first comfort' is the wordplay.
'cabbie's first' becomes 'c' (1st letter of 'cabbie').
'comfort' becomes 'ease' (synonyms).
'c'+'ease'='CEASE'
(Other definitions for cease that I've seen before include "Come to an end" , "Stop, give over" , "Political group" , "Finish, end" , "Desist" .)