Is lazy resulting in a deficiency on board (6)
I believe the answer is:
slacks
'is' is the definition.
The answer and definition can be both to do with social activities as well as being verbs in their -s form.
Maybe you can see an association between them that I don't see?
'lazy resulting in a deficiency on board' is the wordplay.
'lazy resulting in' becomes 'ss' (I am not sure about this - if you are sure you should believe this answer much more).
'a deficiency' becomes 'lack' ('lack' can be a synonym of 'deficiency').
'on board' is an insertion indicator (inserted letters are taken on board).
'ss' going around 'lack' is 'SLACKS'.
Can you help me to learn more?
(Other definitions for slacks that I've seen before include "Pants for casual wear" , "Things to wear" , "Loose casual trousers" , "Works lazily; trousers" , "takes it easy" .)