Seaweed from coastal Galway (4)
I believe the answer is:
alga
'seaweed' is the definition.
(I've seen this before)
'from coastal galway' is the wordplay.
'from' says the answer is hidden in the clue.
'ALGA' is hidden within 'coastal galway'.
(Other definitions for alga that I've seen before include "nuisance on the beach?" , "Kind of seaweed" , "Gala (anag.)" , "Possibly tangle" , "Water plant with no stem or leaves" .)