Yours, Etc.: Origins and Uses of 8 Sign-Offs
1831, American English, "temper," of unknown origin; perhaps originally from figurative use of West Indies dander, dunder "fermentation of sugar," from Spanish redundar "to overflow," from Latin redundare (see redundant).
dander dan·der (dān'dər)
Small scales from the skin, hair, or feathers of an animal, often causing an allergic reaction in sensitive individuals.