1610s, "one who makes spots," agent noun from spot (v.). From 1893 in hunting; 1903 in sense "look-out."
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spot v.
mid-13c., "to mark or stain with spots;" late 14c. as "to stain, sully, tarnish," from spot (n.). Meaning "to see and recognize," is from 1718, originally colloquial and applied to a criminal or suspected person; the general sense is from 1860. Related: Spotted; spotting. Spotted dick "suet pudding with currants and raisins" is attested from 1849.