Doctrine — principle ultimately confined to temporary accommodation (5)
I believe the answer is:
tenet
'doctrine' is the definition.
(tenet is a kind of doctrine)
'principle ultimately confined to temporary accommodation' is the wordplay.
'ultimately' says to take the final letters.
'confined to' is an insertion indicator.
'temporary accommodation' becomes 'tent' (I've seen this before).
The final letter of 'principle' is 'e'.
'e' placed within 'tent' is 'TENET'.
(Other definitions for tenet that I've seen before include "you may believe in it" , "A belief or credo - it's a palindrome" , "Article of belief" , "Doctrine; principle held" , "That's the law" .)