Hostile? Australian against Gaelic? (6)
I believe the answer is:
averse
'hostile?' is the definition.
(I've seen this in another clue)
'australian against gaelic?' is the wordplay.
'australian' becomes 'A'.
'against' becomes 'v' (abbreviation for 'versus').
'gaelic?' becomes 'Erse' (synonyms).
'a'+'v'+'erse'='AVERSE'
(Other definitions for averse that I've seen before include "Disinclined, loath" , "A piece of poetry is reluctant" , "A line of poetry is opposed" , "Disinclined - sounds like a poem" , "Strongly opposed (to something)" .)