IPA: /ˌɪn.dɪˈfɛn.sə.bəl/
KK: /ɪnˈdɛfənˌsəbl/
Something that cannot be justified or defended; it is unreasonable or unacceptable.
His actions were deemed indefensible by the committee.
Indefensible → It is formed from "in-" (meaning not) and "defensibilis" (from Latin "defendere", meaning to defend). The word "indefensible" means not able to be defended or justified.
Think of 'not' ('in-') being able to 'defend' ('defendere') something — that's why indefensible means something that cannot be defended.