A banned or unlawful item.
"The police confiscated the illicit drugs found hidden in his car trunk."
contrary to accepted morality (especially sexual morality) or convention
"an illicit association with his secretary"
contrary to or forbidden by law
"an illegitimate seizure of power"
"illicit trade"
"an outlaw strike"
"unlawful measures"
Not approved by law, but not invalid.
"The judge ruled that while the contract was illicit because it violated zoning laws, it remained valid and enforceable between the parties until the building permits were finally issued."