indefectibly

Etymology tree
Proto-Indo-European *né
Proto-Indo-European *n̥-
Proto-Italic *n̥-
Latin in-bor.
Middle English in-
English in-
Proto-Indo-European *de
Proto-Indo-European *-h₁
Proto-Indo-European *déh₁
Proto-Italic *dē
Latin dē
Latin de-
Proto-Indo-European *dʰeh₁k-
Proto-Indo-European *-yéti
Proto-Indo-European *dʰh₁kyéti
Proto-Italic *θakjō
Proto-Italic *fakjō
Latin facio
Latin dēficiō
Proto-Indo-European *-tus
Proto-Italic *-tus
Latin -tus
Latin dēfectusbor.
English defect
Proto-Indo-European *-tḗr
Proto-Indo-European *-dʰlom
Proto-Indo-European *-dʰlis
Proto-Italic *-ðlis
Latin -bilis
Latin -ibilis
Old French -ibleder.
Middle English -ible
English -ible
English indefectible
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 indefectibly
From indefectible + -ly.