Somebody wanting a spare form? (7)
I believe the answer is:
slimmer
'somebody wanting a spare form?' is the definition.
I can't judge whether this definition defines the answer.
'wanting a spare form?' is the wordplay.
'wanting' means one lot of letters go next to another.
'a spare' becomes 'slim' (I've seen this in another clue).
'form?' becomes 'mer' (I can't justify this - if you can you should give a lot more credence to this answer).
'slim' put next to 'mer' is 'SLIMMER'.
Can you help me to learn more?
(Other definitions for slimmer that I've seen before include "More slender" , "person who's trying to lose weight" , "One losing weight" , "More slenderly built" , "thinner" .)