異母 is read as いぼ (ibo) and means different mother.
いぼ
ibo
いぼまい
half-sister (younger, different mother)
いぼきょうだい
half-sibling (with a different mother)
いじょう
strangeness
いどう
(personnel) change
いせい
isomerism
いみょう
synonym (taxonomy)
いくどうおん
(saying) with one voice
いたん
heresy
ことなる
to differ
いれい
exceptional
いぎ
objection
いろん
different opinion