It's sentimental to most of Twitter (4)
I believe the answer is:
twee
'it's sentimental' is the definition.
(I've seen this before)
'most of twitter' is the wordplay.
'most of' means to remove the last letter.
'twitter' becomes 'tweet' (I've seen this before).
'tweet' with its final letter taken away is 'TWEE'.
'to' is the link.
(Other definitions for twee that I've seen before include "Affectedly dainty or refined" , "Sickly sweet" , "Sentimentally sweet" , "Affectedly cute" , "Overly cute" .)