He's evidently right to go to sea (7)
I believe the answer is:
mariner
'he's' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'evidently right to go to sea' is the wordplay.
'evidently right' becomes 'r' (common abbreviation. I am not sure about the 'evidently' bit.).
'to go to' says to put letters next to each other.
'sea' becomes 'marine' (I've seen this before).
'r' after 'marine' is 'MARINER'.
Can you help me to learn more?
(Other definitions for mariner that I've seen before include "Sea dog" , "Seafarer, old salt" , "Sea-goer, ancient in the poem" , "Man of the sea" , "Person sailing" .)