Outfit includes new tie (4)
I believe the answer is:
knit
'tie' is the definition.
(I've seen this before)
'outfit includes new' is the wordplay.
'outfit' becomes 'kit' (synonyms).
'includes' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'kit' enclosing 'n' is 'KNIT'.
(Other definitions for knit that I've seen before include "Put together" , "Contract; intertwine" , "Unite; use needles" , "Make textiles with needles and wool" , "manufacture clothing?" .)