Briefly recognise lakes and hillock (5)
I believe the answer is:
knoll
'hillock' is the definition.
(synonyms)
'briefly recognise lakes' is the wordplay.
'briefly' means to remove the last letter.
'recognise' becomes 'know' (synonyms).
'lakes' becomes 'll' (L is an abbreviation for lake).
'know' with its final letter removed is 'kno'.
'kno'+'ll'='KNOLL'
'and' is the link.
(Other definitions for knoll that I've seen before include "Small rounded hill" , "Small hill or mound" , "minor eminence" , "Hummock" , "Little hill" .)