A pain, taking pressure from tribe (6)
I believe the answer is:
apache
'tribe' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'a pain taking pressure' is the wordplay.
'pain' becomes 'ache' (ache is a kind of pain).
'taking' indicates putting letters inside.
'pressure' becomes 'p' (scientific abbreviation).
'a'+'ache'='aache'
'aache' placed around 'p' is 'APACHE'.
'from' acts as a link.
Can you help me to learn more?
(Other definitions for apache that I've seen before include "member of tribe" , "A native N. American people" , "Indian brave" , "Geronimo's people" , "Tribal type" .)