Dotty character entering part of church is overtrusting (5)
I believe the answer is:
naive
'overtrusting' is the definition.
(naive can mean overtrusting or credulous)
'dotty character entering part of church' is the wordplay.
'dotty character' becomes 'i' (a lowercase i has a dot on it).
'entering' means one lot of letters goes inside another.
'part of church' becomes 'nave' ('nave' is part of 'church').
'i' placed inside 'nave' is 'NAIVE'.
'is' is the link.
(Other definitions for naive that I've seen before include "Rather too innocent and trusting" , "Innocently trustful" , "childlike" , "Ingenous, easy to gull" , "Artless, innocent" .)