Unusual start in passage (7)
I believe the answer is:
transit
'passage' is the definition.
('transit' can be a synonym of 'passage')
'unusual start in' is the wordplay.
'unusual' indicates an anagram.
'start'+'in'='startin'
'startin' anagrammed gives 'TRANSIT'.
(Other definitions for transit that I've seen before include "The carrying of people etc" , "Travel" , "Pass across/through" , "Conveyance of goods or people - tin star (anag)" , "carriage" .)