Boffin, one enthralled by exotic insect in street? (9)
I believe the answer is:
scientist
'boffin' is the definition.
(I've seen this before)
'one enthralled by exotic insect in street?' is the wordplay.
'one' becomes 'i' (Roman numeral).
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'exotic' indicates anagramming the letters (an unusual form of the letters).
'in' indicates putting letters inside.
'street?' becomes 'st' (abbreviation).
'insect' with letters rearranged gives 'cients'.
'i' put inside 'cients' is 'cientis'.
'cientis' put inside 'st' is 'SCIENTIST'.
(Other definitions for scientist that I've seen before include "Researcher - boffin" , "Eg, a chemist" , "entomologist maybe" , "It's nicest for one engaged in specialist studies" , "`Tis nicest kind of specialist" .)