The compound adjective 'three-level' is a modern English formation, transparently combining two native elements. The first element, 'three', is a fundamental numeral with ancient Indo-European roots, signifying a specific quantity. The second element, 'level', originates from the Latin concept of a balance or scale (libra), which evolved through Old French to denote a flat, even surface and, by metaphorical extension, a stage or degree of attainment. The logic of the compound is purely descriptive, directly applying the ancient numeral to the later metaphorical sense of 'level' to create a term specifying a structure or system with three distinct tiers or stages of operation.

Structure: three (number) + level (degree) - three: From Old English þrīe, þrēo, from Proto-Germanic þrīz, from Proto-Indo-European tréyes. Functions as a cardinal number. - level: From Middle English level, from Old French livel, from Vulgar Latin libellum, from Latin libella (a small balance, level), diminutive of libra (balance, scale). Functions as a noun meaning a relative position, degree, or stage.