A rota devised for main supplier (5)
I believe the answer is:
aorta
'main supplier' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'a rota devised' is the wordplay.
'devised' indicates anagramming the letters.
'rota' is an anagram of 'orta'.
'a'+'orta'='AORTA'
'for' is the link.
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "Main artery from heart" , "Large trunk artery" , "Blood-carrier from a heart" , "Tube" , "Trunk route" .)