Lag or break in slow movement (5)
I believe the answer is:
largo
'slow movement' is the definition.
(I've seen this in another clue)
'lag or break' is the wordplay.
'break' indicates an anagram.
'lag'+'or'='lagor'
'lagor' anagrammed gives 'LARGO'.
'in' is the link.
(Other definitions for largo that I've seen before include "(Musically) slow in tempo and broad in manner" , "Deliberately" , "Moderately slowly" , "Goldfinger part" , "In a slow tempo (mus.)" .)