Naughty mates possibly let off (5)
I believe the answer is:
steam
'let off' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how one could define the other.
'naughty mates' is the wordplay.
'naughty' indicates anagramming the letters.
'mates' is an anagram of 'STEAM'.
'possibly' is the link.
Can you help me to learn more?
(Other definitions for steam that I've seen before include "Kettle emission" , "Gas formed by vaporizing water at 100?C" , "Water-vapour" , "Driving force" , "Mates (anag)" .)