What does "snail" mean?

Additional senses

1. 2.(Mech.) A spiral cam, or a flat piece of metal of spirally curved outline, used for giving motion to, or changing the position of, another part, as the hammer tail of a striking clock.
2. 3.A tortoise; in ancient warfare, a movable roof or shed to protect besiegers; a testudo. [Obs.] They had also all manner of gynes [engines] . . . that needful is [in] taking or sieging of castle or of city, as snails, that was naught else but hollow pavises and targets, under the which men, when they fought, were heled [protected], . . . as the snail is in his house; therefore they cleped them snails. Vegetius (Trans.).
3. 4.(Bot.) The pod of the sanil clover. Ear snail, Edible snail, Pond snail, etc. See under Ear, Edible, etc. -- Snail borer (Zoöl.), a boring univalve mollusk; a drill. -- Snail clover (Bot.), a cloverlike plant (Medicago scuttellata, also, M. Helix); -- so named from its pods, which resemble the shells of snails; -- called also snail trefoil, snail medic, and beehive. -- Snail flower (Bot.), a leguminous plant (Phaseolus Caracalla) having the keel of the carolla spirally coiled like a snail shell. -- Snail shell (Zoöl.), the shell of snail. -- Snail trefoil. (Bot.) See Snail clover, above.