The inscription was partly illegible.
For those of us cursed with illegible scrawls that we laughingly call handwriting, well, that's what computers were made for.
Always plan to have illegible writing or misspellings on several envelopes.
Doctors can get away with illegible scrawls but you can't.
Illegible rebates will often not be processed.
Two words are almost illegible, and the angular print slants in every direction.
A text may become illegible through damp or constant thumbing; portions of it may be torn away; if it is in book form, leaves or whole quires may be detached and either lost or misplaced.