Suit at function making preparations? (9)
I believe the answer is:
spadework
'preparations?' is the definition.
(I've seen this in another clue)
'suit at function' is the wordplay.
'suit' becomes 'spade' (I have seen 'black suit' mean 'spade' so perhaps 'suit' could also mean 'spade').
'at' says to put letters next to each other.
'function' becomes 'work' (synonyms).
'spade'+'work'='SPADEWORK'
'making' is the link.
(Other definitions for spadework that I've seen before include "Routine preparation" , "Routine preparations for an undertaking" , "Necessary preparation - digging?" , "Basic preparations" , "Preparatory labour (in the garden?)" .)