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' indicates putting letters inside (to bore something can mean to drill into it).
'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" .)