Small – little – tiny first dessert (5)
I believe the answer is:
sweet
'dessert' is the definition.
('sweet' can be a synonym of 'dessert')
'small little tiny first' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'little' becomes 'wee' ('wee' can be similar in meaning to 'little'**).
'first' says to take the initial letters.
The initial letter of 'tiny' is 't'.
's'+'wee'+'t'='SWEET'
(Other definitions for sweet that I've seen before include "Pudding" , "Having a sugary taste" , "Term of endearment" , "Pleasing" , "bon-bon" .)