Start rowing in a rotten lake! (5)
I believe the answer is:
broad
'lake' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'start rowing in a rotten' is the wordplay.
'start' means to remove the last letter (I've seen 'start of' mean this).
'rowing' becomes 'row' (synonyms).
'in' is an insertion indicator.
'a rotten' becomes 'bad' (I've seen this before).
'row' with its final letter removed is 'ro'.
'ro' going inside 'bad' is 'BROAD'.
Can you help me to learn more?
(Other definitions for broad that I've seen before include "East Anglian waterway" , "Spacious - tolerant" , "dame" , "not detailed" , "Wide; general" .)