Initially too small: cute! (4)
I believe the answer is:
twee
'cute' is the definition.
(I've seen this before)
'initially too small' is the wordplay.
'initially' says to take the initial letters.
'small' becomes 'wee' ('wee' can be similar in meaning to 'small').
The initial letter of 'too' is 't'.
't'+'wee'='TWEE'
(Other definitions for twee that I've seen before include "Overly precious" , "Excessively pretty" , "Sentimental, quaint" , "Sentimentally pretty" , "Affectedly dainty or quaint" .)