Reminder of archdeacon, one tucking into tart (8)
I believe the answer is:
souvenir
'reminder' is the definition.
(souvenir is a kind of reminder)
'archdeacon one tucking into tart' is the wordplay.
'archdeacon' becomes 'ven' (abbreviation for The Venerable).
'one' becomes 'I' (Roman numeral).
'tucking into' is an insertion indicator.
'tart' becomes 'sour ' (similar in meaning).
'ven'+'i'='veni'
'veni' put into 'sour' is 'SOUVENIR'.
'of' acts as a link.
(Other definitions for souvenir that I've seen before include "Reminder of past events" , "something worth keeping" , "Reminder of holiday" , "Keepsake, memento" , "remember seeing this?" .)