From bēta (“beet”), from Augustus, quoted by Suetonius.
Ponit assidue et pro stulto "baceolum" et pro pullo "pulleiaceum" et pro cerrito "vacerrosum" et "vapide" se habere pro male et "betizare" pro languere, quod vulgo "lachanizare" dicitur
-- Suetonius De Vita Caesarum Liber VIII Divus Augustus 87.2
He also habitually used "baceolus"(dolt) for "stultus"(fool), "pulleiaceus"(darkish) for "pullus"(dark), "vacerrosus"(blockhead) for "cerritus"(mad); also "vapide se habere"(to feel flat) for "male se habere"(to feel bad) and "betizare"(to be like a beet) for "languere"(to be weak) which is "lanchanizare" in vulgar terms
bētīzō (present infinitive bētīzāre, perfect active bētīzāvī, supine bētīzātum); first conjugation