Truss neck with something worn around it, at first (3,4)
I believe the answer is:
tie down
'truss' is the definition.
(synonyms)
'neck with something worn around it at first' is the wordplay.
'neck with' becomes 'down' (both can mean to swallow or drink quickly. I am not sure about the 'with' bit.).
'something worn' becomes 'mantilla' (I've seen this before).
'around' means to look at the middle letters.
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'at first' is a charade indicator (letters next to each other).
The middle of 'mantilla' is 'ti'.
'ti'+'e'='tie'
'down' after 'tie' is 'TIE DOWN'.
(Other definitions for tie down that I've seen before include "Bind by conditions - to widen (anag)" , "Fix; bind by conditions" , "Restrain with ropes" , "Restrict" .)