IPA: /ˌɪn.dɪˈfɛn.sə.bli/
KK: /ɪnˈdɛfənzəbli/
In a way that cannot be defended or justified; without any valid reason or argument.
The decision was made indefensibly, leaving many people confused and upset.
Indefensibly → It is formed from "in-" (meaning not), "defensibilis" (from Latin, meaning defensible or able to be defended), and the suffix "-ly" (meaning in a manner). The word "indefensibly" means in a manner that cannot be defended or justified.
Think of 'not' ('in-') being combined with 'able to be defended' ('defensibilis') — this helps you remember that 'indefensibly' means something that cannot be defended.