Close match, one assumed after dark (7)
I believe the answer is:
nightie
'one assumed after dark' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'close match' is the wordplay.
'close' becomes 'nigh' (similar in meaning).
'match' becomes 'tie' (I've seen this before).
'nigh'+'tie'='NIGHTIE'
Can you help me to learn more?
(Other definitions for nightie that I've seen before include "Female bedwear" , "Clothing worn in bed" , "put on at end of day?" , "Skimpy attire" , "Item worn by women" .)