Calm a boring colleague (5)
I believe the answer is:
allay
'calm' is the definition.
(I've seen this in another clue)
'a boring colleague' is the wordplay.
'boring' means one lot of letters goes inside another (some letters must 'bore' a hole into other letters).
'colleague' becomes 'ally' (ally can mean a colleague or associate).
'a' put inside 'ally' is 'ALLAY'.
(Other definitions for allay that I've seen before include "Diminish or end (fears)" , "Calm fears" , "Marks of blows" , "Diminish (fears/concern)" , "Quell" .)