Answer’s a lot of relaxation beside small lake (7)
I believe the answer is:
respond
'answer's' is the definition.
(synonyms)
'a lot of relaxation beside small lake' is the wordplay.
'a lot of' means to remove the last letter (a lot of but not all of the word).
'relaxation' becomes 'rest' (synonyms).
'beside' is a charade indicator (letters next to each other) (I've seen this in other clues).
'small lake' becomes 'pond' (I've seen this before).
'rest' with its final letter removed is 'res'.
'res'+'pond'='RESPOND'
(Other definitions for respond that I've seen before include "Come back" , "State in reply" , "Write back" , "Reply - react" , "Answer or react" .)