onerous

The word 'onerous' originates from the Latin adjective onerosus, meaning "burdensome," which itself derives from the noun onus (genitive oneris), meaning "load" or "burden." This Latin root can be traced back to the Proto-Indo-European root h₃enh₂-, which carried the sense of "to load" or "to burden." The semantic journey is direct and logical: the literal concept of a physical load evolved into the abstract sense of a heavy responsibility or a difficult, troublesome obligation. The suffix -ous consistently imparts the meaning "full of," thus making 'onerous' literally mean "full of burden."

Structure: oner (burden) + ous (adjective suffix) oner (from Latin onus, meaning "load, burden"); ous (a suffix forming adjectives, from Latin -osus, meaning "full of, characterized by").