Uncommon morsel for a snack? (7)
I believe the answer is:
rarebit
'for a snack?' is the definition.
(I've seen this before)
'uncommon morsel' is the wordplay.
'uncommon' becomes 'rare' (similar in meaning).
'morsel' becomes 'bit' (synonyms).
'rare'+'bit'='RAREBIT'
(Other definitions for rarebit that I've seen before include "Cheesy snack" , "Arbiter of Welsh dish with melted cheese on toast" , "Cheese/toast savoury" , "mouthful?" , "Arbiter (anag) -- snack" .)