Italian ancestor found in the Atlantic, swimming (5)
I believe the answer is:
latin
'atlantic swimming' is the definition.
Although both the answer and definition are adjectives, I don't see how they can define each other.
'italian ancestor found in' is the wordplay.
'italian ancestor' becomes 'lat' (I can't explain this - if you can you should give a lot more credence to this answer).
'found' means one lot of letters go next to another.
'lat'+'in'='LATIN'
'the' is the link.
Can you help me to learn more?
(Other definitions for latin that I've seen before include "Hispanic, for example" , "Language of ancient Rome" , "The language of old Rome" , "Shakespeare's was small, according to Jonson" , "Language of old Romans" .)