Leaning or moving to one side; or the medieval sport of jousting where knights charged at each other on horseback.
From Middle English 'tilten,' possibly from Old English 'tealt' meaning unsteady. The jousting meaning comes from knights 'tilting' their lances at opponents during tournaments.
The phrase 'tilting at windmills' comes from Don Quixote attacking windmills he thought were giants—it's become the perfect phrase for fighting impossible battles, all from a Spanish novel written in 1605!
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