ILLICITLY
illegally, illicitly, lawlessly
(adverb) in an illegal manner; “they dumped the waste illegally”
illegitimately, illicitly
(adverb) in a manner disapproved or not allowed by custom; “He acted illegitimately when he increased the rent fourfold”
Source: WordNet® 3.1
Etymology
Adverb
illicitly (comparative more illicitly, superlative most illicitly)
In an illicit manner; illegally, immorally or inappropriately.
Source: Wiktionary
ILLICIT
Il*lic"it, a. Etym: [L. illicitus; pref. il- not + licitus, p.p. of
licere to be allowed or permitted: cf. F. illicite. See In- not, and
License.]
Definition: Not permitted or allowed; prohibited; unlawful; as, illicit
trade; illicit intercourse; illicit pleasure.
One illicit . . . transaction always leads to another. Burke.
– Il*lic"it*ly, adv.
– Il*lic"it*ness, n.
Source: Webster’s Unabridged Dictionary 1913 Edition