Expand a green meandering around lake (7)
I believe the answer is:
enlarge
'expand' is the definition.
(thesaurus)
'a green meandering around lake' is the wordplay.
'meandering' indicates anagramming the letters.
'around' indicates putting letters inside.
'lake' becomes 'l'.
'a'+'green'='agreen'
'agreen' is an anagram of 'enarge'.
'enarge' placed around 'l' is 'ENLARGE'.
(Other definitions for enlarge that I've seen before include "Blow up" , "Describe in more detail" , "Grow" , "Lengthen" , "Gleaner (anag.)" .)