perilous(s = adj.all) parlous, precarious, touch-and-go - fraught with danger; "dangerous waters"; "a parlous journey on stormy seas"; "a perilous voyage across the Atlantic in a small boat"; "the precarious life of an undersea diver"; "dangerous surgery followed by a touch-and-go recovery"
Derived forms noun peril₃, noun peril₁, noun peril₂, noun perilousness₁

1.  Full of, attended with, or involving, peril; dangerous; hazardous; as, a perilous undertaking. [1913 Webster]
"Infamous hills, and sandy, perilous wilds." [1913 Webster]

2.  Daring; reckless; dangerous. Latimer. [1913 Webster]
"For I am perilous with knife in hand." [1913 Webster]

perilous, adj.
1 full of risk; dangerous; hazardous.
2 exposed to imminent risk of destruction etc.

Derivative:
perilously adv. perilousness n.

Etymology:
ME f. OF perillous f. L periculosus f. periculum: see PERIL

N  danger, peril, insecurity, jeopardy, risk, hazard, venture, precariousness, slipperiness, instability, defenselessness, exposure, vulnerability, vulnerable point, heel of Achilles, forlorn hope, leap in the dark, road to ruin, faciles descensus Averni, hairbreadth escape, cause for alarm, source of danger, rock ahead, breakers ahead, storm brewing, clouds in the horizon, clouds gathering, warning, alarm, apprehension, in danger, endangered, fraught with danger, dangerous, hazardous, perilous, parlous, periculous, unsafe, unprotected &c (safe, protect), insecure, untrustworthy, built upon, sand, on a sandy basis, wildcat, defenseless, fenceless, guardless, harborless, unshielded, vulnerable, expugnable, exposed, open to, aux abois, 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, 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, off one's guard, 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, threatening, ominous, illomened, alarming, explosive, adventurous, incidit in Scyllam qui vult vitare Charybdim, nam tua res agitur paries dum proximus ardet.

N  fear, timidity, diffidence, want of confidence, apprehensiveness, fearfulness, solicitude, anxiety, care, apprehension, misgiving, feeze, mistrust, suspicion, qualm, hesitation, nervousness, restlessness, inquietude, disquietude, worry, concern, batophobia, heartquake, flutter, trepidation, fear and trembling, perturbation, tremor, quivering, shaking, trembling, throbbing heart, palpitation, ague fit, cold sweat, abject fear, mortal funk, heartsinking, despondency, despair, fright, affright, affrightment, boof alarm, dread, awe, terror, horror, dismay, consternation, panic, scare, stampede (of horses), intimidation, terrorism, reign of terror, bug bear, bugaboo, scarecrow, hobgoblin, nightmare, Gorgon, mormo, ogre, Hurlothrumbo, raw head and bloody bones, fee-faw-fum, bete noire, enfant terrible, alarmist, fearing, frightened, in fear, in a fright, haunted with the fear of, afeard, afraid, fearful, timid, timorous, nervous, diffident, coy, faint- hearted, tremulous, shaky, afraid of one's shadow, apprehensive, restless, fidgety, more frightened than hurt, aghast, awe-stricken, horror-stricken, terror-stricken, panic- stricken, awestruck, awe-stricken, horror-struck, frightened to death, white as a sheet, pale, pale as a ghost, pale as death, pale as ashes, breathless, in hysterics, inspiring fear, alarming, formidable, redoubtable, perilous, portentous, fearful, dread, dreadful, fell, dire, direful, shocking, terrible, terrific, tremendous, horrid, horrible, horrific, ghastly, awful, awe-inspiring, revolting, Gorgonian, in terrorem, Int, angels and ministers of grace defend us!, ante tubam trepidat, horresco referens, one's heart failing one, obstupui steteruntque comae et vox faucibus haesit, a dagger of the mind, expertus metuit, fain would I climb but that I fear to fall, fear is the parent of cruelty, Gorgons and hydras and chimeras dire, omnia tuta timens, our fears do make us traitors.

siege perilous