US commando in ocean and lake (4)
I believe the answer is:
seal
'us commando' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'ocean and lake' is the wordplay.
'ocean' becomes 'sea' (synonyms).
'and' says to put letters next to each other.
'lake' becomes 'L' (geographical abbreviation).
'sea'+'l'='SEAL'
'in' is the link.
Can you help me to learn more?
(Other definitions for seal that I've seen before include "Authorise - plug" , "Make waterproof - stamp" , "Fasten with hot wax" , "Imprinted disk affixed to a document" , "Make tight" .)