Sign of hesitation after key change (5)
I believe the answer is:
alter
'change' is the definition.
(synonyms)
'sign of hesitation after key' is the wordplay.
'sign of hesitation' becomes 'er'.
'after' means one lot of letters go next to another.
'key' becomes 'alt' (the Alt keyboard button).
'er' after 'alt' is 'ALTER'.
(Other definitions for alter that I've seen before include "Alert to change" , "Change, maybe later" , "Metamorphose" , "Adapt" , "Vary" .)