Straight man loses sight of what gets repeated (6)
I believe the answer is:
mantra
'straight' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mantra that I've seen before include "what one keeps repeating" , "repeating phrase" , "Sacred words used as incantation" , "Vedic hymn; slogan frequently repeated" , "Word or phrase repeated as aid to concentration" .)