Short message, cute (4)
I believe the answer is:
twee
'cute' is the definition.
(I've seen this before)
'short message' is the wordplay.
'short' means to remove the last letter.
'message' becomes 'tweet' (type of online message).
'tweet' with its last letter taken away is 'TWEE'.
(Other definitions for twee that I've seen before include "Overly precious" , "Affectedly cute" , "Excessively sentimental" , "Affectedly dainty or quaint" , "Affected quaint" .)