IPA: /ɪˈlɛdʒɪbli/
KK: /ɪˈlɛdʒɪbli/
In a way that cannot be read or understood clearly.
The note was written illegibly, making it hard to understand.
Illegibly → It is formed from "il-" (meaning not), "legere" (meaning to read), and "-bly" (meaning in a manner). The word "illegibly" means in a manner that cannot be read or is not readable.
Think of 'not' ('il-') being combined with 'read' ('legere') to remember that 'illegibly' means something that cannot be read.