tilt at windmills, to contend against imaginary opponents or injustices. Also, fight with windmills.
Origin: 1300–50; Middle English tylten to upset, tumble < Scandinavian; compare dialectal Norwegian tylta to tiptoe, tylten unsteady; akin to Old English tealt unsteady, tealtian to totter, amble, Middle Dutch touteren to sway
"a joust, a combat," 1511, perhaps from tilt (v.) on the notion of "to lean" into an attack, but the word originally seems to have been the name of the barrier which separated the combatants, which suggests connection with tilt in an earlier meaning "covering of coarse cloth,
an awning" (c.1440), which is probably from tilt (v.), but perhaps related to or influenced by tent, or it may be from a Gmc. source akin to O.E. beteldan "to cover." The verb is recorded from 1595. Hence, also full tilt (c.1600).