Garment that’s almost neckwear (7)
I believe the answer is:
nightie
'garment' is the definition.
(I've seen this before)
'almost neckwear' is the wordplay.
'almost' becomes 'nigh' ('nigh' can be a synonym of 'almost').
'neckwear' becomes 'tie' (tie is a kind of neckwear).
'nigh'+'tie'='NIGHTIE'
'that's' is the link.
(Other definitions for nightie that I've seen before include "Lingerie item" , "What retiring lady assumes" , "Bedtime attire" , "covering for retired person" , "Late shift perhaps" .)