[[t]ˈæl kəˌlaɪ[/t]] n. pl. -lis, -lies, adj.
1) chem.
a) any of various bases, the hydroxides of the alkali metals and of ammonium, that neutralize acids to form salts and turn red litmus paper blue
b) any of various other active bases, as calcium hydroxide
2) agr. a soluble mineral salt or a mixture of soluble salts, present in some soils, esp. in arid regions, and detrimental to the growing of most crops
3) chem. alkaline
Etymology: 1300–50; < MF alcali < dial. Ar al-qalī, saltwort ashes

From formal English to slang. 2014.