fatso

The word 'fatso' is a modern American English slang coinage from the mid-20th century. It is a compound formed directly from the descriptive English adjective 'fat', which itself has ancient Germanic roots tracing back to a Proto-Indo-European form meaning 'to blow, swell'. The appended '-so' suffix is not a classical morpheme but a colloquial, often pejorative, noun-forming element used to create informal nicknames, implying a person characterized by the preceding trait. The term's logic is transparently literal, combining a direct physical descriptor with a familiar slang ending to produce a label for an overweight individual, typically used in a derogatory or teasing manner.

Structure: fat (adjective) + so (noun suffix) - fat: From Old English fǣtt (fatted, plump). An adjective describing someone or something with a lot of flesh or excess body weight. - so: A slang suffix of unknown, possibly arbitrary, formation, used to create a familiar, often derogatory, nickname or label (cf. 'bozo', 'wacko').