Definition from Wiktionary, the free dictionary
eutectic (not comparable)
- Describing the chemical composition and/or temperature of a mixture of substances that gives the lowest temperature at which the mixture becomes fully molten. A further requirement is that that temperature is lower than the melting point of any of the pure component substances.
- (chemistry) Describing the thermodynamic equilibrium conditions where a liquid coexists with two solid phases.
eutectic (plural eutectics)
- A material that has the composition of a eutectic mixture or eutectic alloy
- The temperature of the eutectic point
Usage notes 
- Use with the indefinite article is mixed. The dominant usage seems to favour "a eutectic", although "an eutectic" can be found in some texts.
- The Oxford English Dictionary