Spiritual teacher with friend had nuts (6)
I believe the answer is:
buddha
'spiritual teacher' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'with friend had nuts' is the wordplay.
'with' indicates putting letters inside.
'friend' becomes 'bud' (shortly for buddy).
'nuts' indicates an anagram (nuts can mean crazy).
'had' is an anagram of 'dha'.
'bud' placed within 'dha' is 'BUDDHA'.
Can you help me to learn more?
(Other definitions for buddha that I've seen before include "statue in temple" , "Person who has achieved perfect enlightenment" , "The philosopher Gautama who founded a great eastern religion" , "Siddhartha Gautama's title" , "Holy man of Indian religion" .)