As one enters Cambs city, without difficulty (6)
I believe the answer is:
easily
'without difficulty' is the definition.
('easily' can be a synonym of 'without difficulty')
'as one enters cambs city' is the wordplay.
'one' becomes 'i' (Roman numeral).
'enters' is an insertion indicator.
'cambs city' becomes 'ely' (I've seen this before).
'as'+'i'='asi'
'asi' put into 'ely' is 'EASILY'.
(Other definitions for easily that I've seen before include "Very probably" , "without a hitch?" , "Simply" , "Effortlessly" , "Without much difficulty" .)