More hostile French company welcomed by Irish (5)
I believe the answer is:
icier
'more hostile' is the definition.
(icy can mean hostile)
'french company welcomed by irish' is the wordplay.
'french company' becomes 'cie' (abbreviation of the french 'compagnie').
'welcomed by' indicates putting letters inside (letters welcomed inside).
'irish' becomes 'IR' (abbreviation).
'cie' put within 'ir' is 'ICIER'.
(Other definitions for icier that I've seen before include "More glacial" , "Colder even than 31 Across" , "More reserved" , "More treacherous" , "rather cold" .)