The word 'undependable' is a modern English construction built from three distinct morphemes. The core, 'depend,' originates from the Latin dependēre, literally "to hang down from," which evolved metaphorically to mean "to rely upon." The suffix '-able,' from Latin -ābilis, attaches to verbs to create adjectives indicating a capacity or worthiness. Finally, the Old English negative prefix 'un-' is prefixed to negate the entire concept. Thus, the literal morphemic logic "not capable of being relied upon" directly and transparently yields the modern abstract meaning of unreliability.

Structure: un (not) + depend (rely) + able (capable of) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - depend: A verb of Latin origin (dependēre, from de- "down" + pendēre "to hang"). It functions as the core root meaning "to rely." - able: A suffix of Latin origin (-ābilis), forming adjectives meaning "capable of, fit for, or worthy of."