Supple and gracefully flexible; bending with ease and strength, as a branch bends without breaking, or a body moves without friction (literary; also general). About motion, not measure. Agility made visible.

From Old English līthe “gentle, mild; pliant,” related to a Germanic family of words for softness and ease. The meaning has narrowed from temperament to body, but the original gentleness still clings to the modern sense.