Capsule the Spanish left, swallowed by family dog, perhaps (6)
I believe the answer is:
pellet
'capsule' is the definition.
(both can mean a rounded mass of something)
'the spanish left swallowed by family dog perhaps' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'left' becomes 'l' (common abbreviation).
'swallowed by' is an insertion indicator.
'family dog perhaps' becomes 'pet' (dogs are often kept as pets).
'el'+'l'='ell'
'ell' going into 'pet' is 'PELLET'.
(Other definitions for pellet that I've seen before include "Piece of shot for gun" , "Small rounded mass" , "Small ball of iron" , "Shot -- slug" , "Small pill" .)