The word vacuous originates from the Latin vacuus, meaning "empty, void, or free from," which itself derives from the verb vacare, "to be empty." The core concept of emptiness was carried directly into English, where it first described physical void. Over time, the meaning expanded metaphorically to describe an emptiness of thought, expression, or substance. The suffix -ous, indicating a quality or state, transforms the root into an adjective, thus characterizing something as being full of emptiness, whether literal or intellectual.

Structure: vacu (empty) + ous (adjective suffix) - vacu: From Latin vacuus, meaning "empty, void, free from." - ous: A suffix forming adjectives, from Latin -osus, meaning "full of, characterized by."