Small measure in church (4)
I believe the answer is:
inch
'small measure' is the definition.
(small length measurement)
'in church' is the wordplay.
'church' becomes 'ch' (abbreviation on maps etc).
'in'+'ch'='INCH'
(Other definitions for inch that I've seen before include "Move along slowly" , "Non-metric measure" , "Move forward slowly and carefully" , "One-twelfth of a foot" , "nose" .)