Invar

[ in-vahr ]
/ ɪnˈvɑr /

Trademark.

a brand of iron alloy containing 35.5 percent nickel and having a very low coefficient of expansion at atmospheric temperatures.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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British Dictionary definitions for invar

Invar
/ (ɪnˈvɑː) /

noun

trademark an alloy containing iron (63.8 per cent), nickel (36 per cent), and carbon (0.2 per cent). It has a very low coefficient of expansion and is used for the balance springs of watches, etc

Word Origin for Invar

C20: shortened from invariable
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