The word 'useable' is a modern English formation built upon the well-established verb 'use'. The root 'use' traces back to Latin uti, meaning to employ or benefit from something, which evolved into the Old French user before entering English. The suffix '-able', of Latin origin via French, is productively attached to verbs to create adjectives meaning "capable of being [verbed]." Therefore, the literal construction "capable of being used" directly and logically yields the modern meaning of something being fit for service or practical application.

Structure: use (to employ) + able (capable of) - use: From Old French user, from Latin usus (use, custom, skill), from the verb uti (to use). Functions as the core verb root. - able: From Old French -able, from Latin -abilis (capable of, fit for), an adjective-forming suffix.