pref ‧ e ‧ ren ‧ tial /ˌprefəˈrenʃ ə l◂/ BrE AmE adjective [only before noun]
[ Word Family: adverb : ↑ preferably , ↑ preferentially ; adjective : ↑ preferable , ↑ preferential ; verb : ↑ prefer ; noun : ↑ preference ]
preferential treatment, rates etc are deliberately different in order to give an advantage to particular people:
preferential credit terms for reliable borrowers
—preferentially adverb