Last job unchanged in foundation? (5)
I believe the answer is:
basis
'foundation?' is the definition.
(I know that basis is a type of foundation)
'last job unchanged' is the wordplay.
'last' indicates one should take the final letters.
'unchanged' becomes 'as is' (I've seen this before).
The final letter of 'job' is 'b'.
'b'+'asis'='BASIS'
'in' acts as a link.
(Other definitions for basis that I've seen before include "Form of support" , "Underlying support for a theory" , "grounds" , "Foundation, fundament" , "Principal element" .)