1) Alloy 2) Alloy of iron and nickel 3) Alloy of nickel and iron 4) Metal 
Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel–iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). The name Invar comes from the word invariable, referring to its relative lack of expansion or contraction with temperature changes. It was invented in 1896 by Swiss scientist Charles Édoua...
alloy of iron that expands very little when heated; it contains 64 percent iron and 36 percent nickel. Invar was formerly used for absolute ... [4 related articles]
Invar is an alloy of iron and nickel.
[n] - (trademark) an alloy of iron and nickel having a low coefficient of thermal expansion
An alloy having practically no expansion when heated; 36% Ni, 0.5% Mn, 0.2% C, and the balance Fe.
Low thermal expansion alloy of iron and nickel. Typically 36% Nickel and 64% Iron.
A nickel iron containing 36 per cent of nickel. It has an exceedingly low rate of expansion and has a high resistance to water corrosion.
a brand of iron alloy containing 35.5 percent nickel and having a very low coefficient of expansion at atmospheric temperatures.