Overly trusting (5)
I believe the answer is:
naive
'overly trusting' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for naive that I've seen before include "Lack of experience, innocent" , "Innocently trustful" , "Excessively trusting or innocent" , "Ingenuous and gullible" , "Ingenuous and credulous" .)