Ultimately hostile in a sense, practising a form of discrimination (6)
I believe the answer is:
ageist
'practising a form of discrimination' is the definition.
(ageism is a type of discrimination)
'ultimately hostile in a sense' is the wordplay.
'ultimately' says to take the final letters.
'in' indicates putting letters inside.
'sense' becomes 'gist' (I've seen this in another clue).
The last letter of 'hostile' is 'e'.
'a'+'gist'='agist'
'e' inserted into 'agist' is 'AGEIST'.
(Other definitions for ageist that I've seen before include "Person biased against old people" , "One prejudiced on grounds of age" , "making it hard for the elderly" , "knocking down the old" , "Discriminating on the basis of years lived" .)