boob

The word "boob" in the sense of a breast is a slang term that emerged in the early 20th century. It is believed to derive from the earlier English dialect word "bubby," a childish or familiar term for the breast, which itself may be a reduplication imitative of a baby's babbling. The semantic connection to foolishness, first recorded in the early 1900s, likely comes from the unrelated American slang "booby," meaning a stupid person, which entered English in the late 16th century possibly from the Spanish "bobo" (fool). Thus, the modern word "boob" represents a convergence of two distinct slang streams, one for a body part and one for a simpleton, unified by their informal and slightly derogatory tone.

The word is a simplex form. It is a reduplication or alteration of the earlier slang term "bubby," which itself is likely a baby-talk alteration of "breast." Its origin is imitative or expressive, not built from classical roots.