Post, unfortunately, lost the tights (8)
I believe the answer is:
'tights' is the definition.
(I know this)
'post unfortunately lost' is the wordplay.
'post' becomes 'mail' (synonyms).
'unfortunately' is an anagram indicator (a bad or unfortunate spelling).
'lost' with letters rearranged gives 'lots'.
'the' is the link.
(Another definition for maillots that I've seen is " ballet tights".)