Voluntary work of a speculative kind with number leaving (8)
I believe the answer is:
optional
'voluntary' is the definition.
(I've seen this before)
'work of a speculative kind with number leaving' is the wordplay.
I cannot quite understand how this works, but
'work' could be 'op' (common abbreviation for 'opus') and 'op' is present in the answer.
'of' could be 'o' and 'o' is found within the answer.
'a' is present in the answer.
'number' could be 'l' (L is an example) and 'l' is present in the answer.
The remaining letters 'tin' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for optional that I've seen before include "something extra?" , "Voluntary - not required" , "Such as one can take or leave" , "Not compulsory, discretionary" , "Elective, as you choose" .)