Involving or causing danger or risk; liable to hurt or harm:
— A dangerous criminal.
— A dangerous bridge.
— Unemployment reached dangerous proportions.

synonym: unsafe.

Roget 665: in danger etc. n.; endangered etc. v.; fraught with danger; dangerous, hazardous, perilous, parlous, periculous^†; unsafe, unprotected etc. (safe, protect) etc. 664; insecure.    untrustworthy; built upon.   sand, on a sandy basis; wildcat.    defenseless, fenceless, guardless^†, harborless; unshielded; vulnerable, expugnable^†, exposed; open to etc. (liable) 177.    aux abois [Fr.], at bay; on the wrong side of the wall, on a lee shore, on the rocks.    at stake, in question; precarious, critical, ticklish; slippery, slippy; hanging by a thread etc. v.; with a halter round one's neck; between the hammer and the anvil, between Scylla and Charybdis, between a rock and a hard place, between the devil and the deep blue sea, between two fires; on the edge of a precipice, on the brink of a precipice, on the verge of a precipice, on the edge of a volcano; in the lion's den, on slippery ground, under fire; not out of the wood.    unwarned, unadmonished, unadvised, unprepared etc. 674; off one's guard etc. (inexpectant) 508^†.    tottering; unstable, unsteady; shaky, top-heavy, tumbledown, ramshackle, crumbling, waterlogged; helpless, guideless^†; in a bad way; reduced to the last extremity, at the last extremity; trembling in the balance; nodding to its fall etc. (destruction) 162.    threatening etc. 909; ominous, illomened; alarming etc. (fear) 860; explosive.    adventurous etc. (rash) 863, (bold) 861.    ... show more

Polish: niebezpieczny

Causing fear or anxiety by threatening great harm:
— A dangerous operation.

synonyms: grave, grievous, life-threatening, serious, severe.

Polish: groźny