Roman sea-horse? (4)
I believe the answer is:
mare
This could be a double definition.
'roman sea' is the first definition.
'mare' can be an answer for 'sea' (I've seen this before). I'm not certain of the 'roman' bit.
'horse?' is the second definition.
(mare is a kind of horse)
Can you help me to learn more?
(Other definitions for mare that I've seen before include "A night-time strangler" , "Adult female zebra" , "Nag" , "Female quadruped" , "Adult female horse" .)