IPA: /ɪnˈkɒnvɜːtəbli/
KK: /ɪnˈkɒnvɜːtəbli/
In a way that cannot be changed or converted into something else.
The rules were inconvertibly set, leaving no room for negotiation.
Inconvertibly → It is formed from "in-" (meaning not) and "convertible" (from Latin "convertere", meaning to turn around or change). The suffix "-ly" indicates the manner of something. Thus, "inconvertibly" means in a manner that cannot be changed or turned into something else.
Think of 'not changing' ('in-') something that is 'able to be turned' ('convertible'). This helps you remember that inconvertibly means something that cannot be changed.