disputably

Etymology tree
Proto-Indo-European *dwóh₁
Proto-Indo-European *d(w)is-
Proto-Italic *dis-
Latin dis-
Latin putus
Proto-Indo-European *-h₂
Proto-Indo-European *-éh₂
Proto-Indo-European *-yéti
Proto-Indo-European *-eh₂yéti
Proto-Italic *-āō
Latin -ō
Latin putō
Latin disputo
Proto-Indo-European *-tḗr
Proto-Indo-European *-dʰlom
Proto-Indo-European *-dʰlis
Proto-Italic *-ðlis
Latin -bilis
Latin disputābilislbor.
English disputable
Proto-Indo-European *leyg-der.
Proto-Germanic *līkąder.
Proto-Germanic *-līkaz
Proto-Germanic *-ê
Proto-Germanic *-līkê
Proto-West Germanic *-līkē
Old English -līċe
Middle English -ly
English -ly
English disputably
From disputable + -ly, equivalent to dispute + -ably.