A lake to rant about? (4)
I believe the answer is:
tarn
'a lake' is the definition.
(I know that tarn is a type of lake)
'rant about?' is the wordplay.
'about?' is an anagram indicator (I've seen 'about' mean this).
'rant' anagrammed gives 'TARN'.
'to' acts as a link.
(Other definitions for tarn that I've seen before include "Scottish mountain lake" , "Small mountain lake" , "High water" , "Mountain pool: French department" .)