IPA: /ˌɪndɪˈspɛnsəbli/
KK: /ɪnˌdɪspənˈsæbli/
In a way that is absolutely necessary or essential.
Water is indispensably important for all living beings.
Indispensably → It is formed from "in-" (meaning not) and "dispensable" (from Latin "dispensabilis", meaning able to be dispensed or managed). The suffix "-ly" (meaning in a manner) indicates the manner of being. Thus, "indispensably" means in a manner that is not able to be dispensed with or absolutely necessary.
Think of something that is 'not able to be managed without' — 'in-' means not, and 'dispensable' means able to be managed. This helps you remember that 'indispensably' refers to something that is absolutely necessary.