Reply from Greeks oddly ignored small body of water (7)
I believe the answer is:
respond
'reply' is the definition.
('respond' can be a synonym of 'reply')
'greeks oddly ignored small body of water' is the wordplay.
'oddly ignored' indicates alternate letters.
'small body of water' becomes 'pond' (I've seen this before).
The alternate letters of 'greeks' are 'res'.
'res'+'pond'='RESPOND'
'from' is the link.
(Other definitions for respond that I've seen before include "Write back" , "Reply - react" , "Come back" , "Answer or react" , "State in reply" .)