means To deliberately provoke, bait, or harass people online with inflammatory or off-topic posts — or the person who does so; also, in older usage, the lumbering monster of Norse folklore.

from Two threads braided into one modern word. The monster comes from Old Norse 'troll,' a malevolent being of Scandinavian myth, lurking in mountains and (in later folklore) under bridges. The internet sense, however, comes from a different root: the fishing technique of 'trolling,' dragging baited lines slowly through the water to see what bites — itself from Old French 'troller,' to wander or rove in search of game. Early internet users spoke of 'trolling for newbies,' baiting the gullible — and the happy coincidence with the bridge-dwelling beast meant the two meanings collapsed gleefully into one.