Only half delivery, it’s true (4)
I believe the answer is:
very
'true' is the definition.
(thesaurus)
'only half delivery' is the wordplay.
'only half' means to take half the letters.
'delivery' with half the letters taken is 'VERY'.
'it's' is the link.
(Other definitions for very that I've seen before include "light, perhaps" , "To a high degree or extent" , "Real" , "Exceedingly" , "Exactly, really" .)