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definitions

dangerous

[deyn-jer-uh s, deynj-ruh s]
adjective
  1. full of danger or risk; causing danger; perilous; risky; hazardous; unsafe.
  2. able or likely to cause physical injury: a dangerous criminal.

Origin of dangerous

1175–1225; Middle English da(u)ngerous domineering, fraught with danger < Old French dangereus threatening, difficult, equivalent to dangier (see danger) + -eus -ous
Related formsdan·ger·ous·ly, adverbdan·ger·ous·ness, nounnon·dan·ger·ous, adjectivenon·dan·ger·ous·ly, adverbnon·dan·ger·ous·ness, nounqua·si-dan·ger·ous, adjectivequa·si-dan·ger·ous·ly, adverbsem·i·dan·ger·ous, adjectivesem·i·dan·ger·ous·ly, adverbsem·i·dan·ger·ous·ness, nounun·dan·ger·ous, adjectiveun·dan·ger·ous·ly, adverb
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for undangerous

dangerous

adjective
  1. causing danger; perilous
Derived Formsdangerously, adverbdangerousness, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for undangerous

dangerous

adj.

early 13c., "difficult, arrogant, severe" (the opposite of affable), from Anglo-French dangerous, Old French dangeros (12c., Modern French dangereux), from danger (see danger).

In Chaucer, it means "hard to please, reluctant to give;" sense of "full of danger, risky" is from late 15c. Other words used in this sense included dangersome (1560s), dangerful (1540s). Related: Dangerously.

Online Etymology Dictionary, © 2010 Douglas Harper
Idioms and Phrases with undangerous

dangerous

see little knowledge is a dangerous thing; live dangerously.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.