Impossible to break; able to withstand rough usage: unbreakable plates. (adjective)
Able to withstand an attempt to break. Used of a horse.(adjective)
An article or object that is not easily broken.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "unbreakable" in a sentence
"My last two pairs of lenses, both Varilux Comfort, one polarized, one clear, both in unbreakable polycarbonate, with non-reflective coatings, cost US$860 from a small private optician in New England."
"Arrow-22 had to be more than just a question mark in his notebook, virtually an unknown quantity to whom he had pledged his help with the Council - Like the high ranks of the Patrol, the various Lensmen elite, he prized his honor as beyond compromise, his word unbreakable, his promises as pledges to be kept."
"Bush treated this pre-eminence the way a naughty boy treats a plate marked "unbreakable" -- he took it as a challenge."