Solemn vows (5)
I believe the answer is:
oaths
'solemn vows' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for oaths that I've seen before include "Imprecations" , "professions of loyalty" , "Swear words" , "Solemn promises or curses" , "Solemn sworn promises" .)