ILLEGIBLY
illegibly, undecipherably, unreadably
(adverb) in an illegible manner; “this student writes illegibly”
Source: WordNet® 3.1
Etymology
Adverb
illegibly (comparative more illegibly, superlative most illegibly)
In a manner that produces illegible results.
The doctor illegibly scrawled his signature: if it weren't on his letterhead, no-one would know who had written it.
Source: Wiktionary
ILLEGIBLE
Il*leg"i*ble, a.
Definition: Incapable of being read; not legible; as, illegible
handwriting; an illegible inscription.
– Il*leg"i*ble*ness, n.
– Il*leg"i*bly, adv.
Source: Webster’s Unabridged Dictionary 1913 Edition