Valet's sniggering gives offence (12)
I believe the answer is:
manslaughter
'offence' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'valet's sniggering' is the wordplay.
'valet's' becomes 'man's' ('man' can be a synonym of 'valet').
'sniggering' becomes 'laughter' (I can't justify this - if you can you should believe this answer much more).
'mans'+'laughter'='MANSLAUGHTER'
'gives' is the link.
Can you help me to learn more?
(Other definitions for manslaughter that I've seen before include "Killing without malice" , "Crime of unpremeditated killing" , "slaying" , "Homicide without malice aforethought" , "Unlawful killing" .)