Motif in rousing song without an echo (5)
I believe the answer is:
theme
'motif' is the definition.
('theme' can be a synonym of 'motif')
'rousing song without an echo' is the wordplay.
'rousing song' becomes 'anthem' (I've seen this before).
'without' is a deletion indicator.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'anthem' with 'an' taken away is 'them'.
'them'+'e'='THEME'
'in' is the link.
(Other definitions for theme that I've seen before include "Main idea or topic" , "Subject matter, topic" , "basis for variations" , "Leitmotiv" , "idea of the work" .)