Tristan's moving passage? (7)
I believe the answer is:
transit
'passage?' is the definition.
(I know that passage can be written as transit)
'tristan's moving' is the wordplay.
'moving' indicates anagramming the letters.
'tristan' is an anagram of 'TRANSIT'.
(Other definitions for transit that I've seen before include "Passage of planet across the disc of the sun" , "Act of passing across" , "Change" , "Pass across/through" , "Pass through; van" .)