Collocations for illegal - adj.

be
become
remain
declare sth, deem sth, make sth, rule sth
Their action was ruled illegal by the International Court.
The sale of these knives should be made illegal.

highly
blatantly
blatantly illegal counter-intelligence methods

clearly
Such acts are clearly illegal.

strictly (esp. BrE), totally
possibly, potentially
allegedly
technically
Prize-fighting remained popular, though technically illegal.

Illegal is used with these nouns:
abortion, act, activity, alien, conduct, copy, dealings, detention, discrimination, disposal, drug, entry, eviction, export, fishing, gambling, hunting, immigrant, immigration, import, ivory, labour, migrant, migration, narcotic, occupation, parking, possession, racket, sale, search, settlement, shipment, smuggling, strike, subsidy, substance, trade, trading, traffic, transaction, use, weapon, worker