The Collaborative International Dictionary of English v.0.48:
Effloresce \Ef`flo*resce"\, v. i. [imp. & p. p. Effloresced;
p. pr. & vb. n. Efflorescing.] [L. efflorescere to bloom,
blossom; ex + florescere to begin to blossom, incho., fr.
florere to blossom, fr. flos a flower. See Flower.]
1. To blossom forth. --Carlyle.
2. (Chem.) To change on the surface, or throughout, to a
whitish, mealy, or crystalline powder, from a gradual
decomposition, esp. from the loss of water, on simple
exposure to the air; as, Glauber's salts, and many others,
3. To become covered with a whitish crust or light
crystallization, from a slow chemical change between some
of the ingredients of the matter covered and an acid
proceeding commonly from an external source; as, the walls
of limestone caverns sometimes effloresce with nitrate of
calcium in consequence of the action of nitric acid formed
in the atmosphere.