By a lake on front of grassy bank (9)
I believe the answer is:
alongside
'by' is the definition.
(I've seen this before)
'a lake on front of grassy bank' is the wordplay.
'lake' becomes 'l'.
'front of' says to take the initial letters.
'bank' becomes 'side' (synonyms).
The initial letter of 'grassy' is 'g'.
'a'+'l'+'on'+'g'+'side'='ALONGSIDE'
(Other definitions for alongside that I've seen before include "Aligned so as to be next to, as ship moored to pier" , "Adjacent to" , "Parallel to" , "Next to, another boat say" , "Juxtaposed" .)