- Refrain ‘chorus of a song’  and refrain ‘desist’  are different words. The former comes via Old French refrain from Provençal refranh. This was a derivative of the verb refranhar, which went back via Vulgar Latin *refrangere to Latin refringere ‘break off’ (source of English refract ). The etymological notion underlying the word is that the chorus of a song ‘breaks off’ and then resumes. Refrain ‘desist’ is descended from Latin refrēnāre ‘hold back’, a compound verb formed from the prefix re- ‘back’ and frēnum ‘bridle’. It reached English via Old French refrener. => FRACTION, REFRACT
The Hutchinson dictionary of word origins. 2013.