Fatuous derives from the Latin fatuus meaning "foolish." It sounds like it should have something to do with being fat, but it actually has no relation to size.

What is the root of infatuation?

The first records of the word infatuation come from the mid-1600s. It ultimately comes from the Latin verb infatuāre, from fatuus, meaning “fatuous” or “foolish.” When it's used in the context of a romantic interest, an infatuation is often like an intense crush—one that consumes your every thought.

What is meant by fatuous?

: complacently or inanely foolish : silly a fatuous remark a fatuous socialite with a near-pathological love of parties and shopping— Janet Maslin.