More foamy like that, a breakwater perhaps (7)

'more foamy' is the definition.
Although both the answer and definition are comparative adjectives, I can't understand how they can define each other.

'that a breakwater perhaps' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'breakwater' could be 'pier' (I've seen this before) and 'pier' is found within the answer.
The remaining letters 'so' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).

'like' acts as a link.

Can you help me to learn more?