Perhaps a tiny portion with no starter (7)
I believe the answer is:
article
'perhaps a' is the definition.
('a' is the indefinite article in English)
'tiny portion with no starter' is the wordplay.
'tiny portion' becomes 'particle' (I've seen this before).
'with no starter' means to remove the first letter.
'particle' with its first letter removed is 'ARTICLE'.
(Other definitions for article that I've seen before include "Definite or indefinite determiner" , "'The', definitely" , "What journalist writes" , "Eg, a, an or the" , "Division" .)