Use the word dangerous to describe anything that can potentially cause serious harm, like a snarling pit bull or an icy, treacherous road.

The earliest meaning of the word dangerous was "difficult or arrogant." When Geoffrey Chaucer wrote "The Canterbury Tales" in the 1300s, he used dangerous to mean "hard to please." Gradually the meaning changed, so that by the late fifteenth century, dangerous meant "liable to cause hurt" or "risky." Just as popular were two other danger-related words that we don't use anymore today: dangersome and dangerful, which at the time could be used interchangeably with dangerous.

Definitions of dangerous
  1. adjective
    involving or causing danger or risk; liable to hurt or harm
    “a dangerous criminal”
    “a dangerous bridge”
    “unemployment reached dangerous proportions”
    synonyms: unsafe
    moving at very high speed
    chanceful, chancy, dicey, dodgy
    of uncertain outcome; especially fraught with risk
    (of persons) dangerously reckless or violent as from urgency or despair
    hazardous, risky, wild
    involving risk or danger
    intended to entrap
    biting or given to biting
    on the hook
    caught in a difficult or dangerous situation
    parlous, perilous, precarious, touch-and-go
    fraught with danger
    self-destructive, suicidal
    dangerous to yourself or your interests
    treacherous, unreliable
    dangerously unstable and unpredictable
    insecure, unsafe
    lacking in security or safety
    susceptible to attack
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    free from danger or the risk of harm
    not causing or capable of causing harm
    not injured physically or mentally
    eliminating danger by compensating automatically for a failure or malfunction
    off the hook
    freed from danger or blame or obligation
    risk-free, riskless, unhazardous
    thought to be devoid of risk
    safe and sound, unhurt
    free from danger or injury
    free from danger or risk
    immune to attack; impregnable
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  2. adjective
    causing fear or anxiety by threatening great harm
    “a dangerous operation”
    synonyms: grave, grievous, life-threatening, serious, severe
    being in or verging on a state of crisis or emergency
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