Show patience when a wit is being clever (4)
I believe the answer is:
wait
'show patience' is the definition.
(I've seen this in another clue)
'a wit is being clever' is the wordplay.
'is being clever' is an anagram indicator.
'a'+'wit'='awit'
'awit' with letters rearranged gives 'WAIT'.
'when' is the link.
(Other definitions for wait that I've seen before include "Delay, stand by" , "Be patient" , "Linger behind" , "Watchman" , "Period of delay" .)