late 14c., "practitioner," agent noun from meddle (v.). Meaning "one who interferes, a nuisance" is mid-15c.
early 14c., "to mingle, blend, mix," from Old North French medler (Old French mesler, 12c., Modern French mêler) "to mix, mingle, to meddle," from Vulgar Latin *misculare (source of Provençal mesclar, Spanish mezclar, Italian mescolare, meschiare), from Latin miscere "to mix" (see mix (v.)). From late 14c. as "busy oneself, be concerned with, engage in;" also disparagingly "interfere, be officious, make a nuisance of oneself" (the notion is of meddling too much). From mid-14c. to 1700, it also was a euphemism for "have sexual intercourse." Related: Meddled; meddling.