regillus.

From regō or rēx. The form is consistent with a derivation from rēx (“king”) via rēgīna (“queen, female member of a royal household”) with contraction of -īn- + -lus to -īllus; compare ovīllus, suīllus, bovīllus. This derivation seems to fit the use in Plautus, which seems similar in sense to rēgius (“magnificent”), and Nonius supposes the word to be a diminutive of rēgius. However, this etymology does not clearly explain why the word was apparently used to refer to some specific garment. An alternative hypothesis holds that it originated primarily as a derivative of the verb regō, with any apparent connection to rēx being a secondary allusion or play on words. In this case, the form might represent a construction such as *rēgulus + -lus (compare rēgula), and the original sense is assumed to have been something like "woven vertically". Compare the use of rēctus in Pliny Natural History 8.194, "Ea prima texuit rectam tunicam, quales cum toga pura tironi induuntur novaeque nuptae." This etymology might be given by Festus, depending on how the passage is punctuated and interpreted. Radicke 2023 supports the derivation from regō along the lines of rēgula, but does not accept the explanation (based on Festus and Pliny) that this referred to weaving style, or the equation of the term with rēctus, or the assumption that this was ever a traditional type of Roman garment. Radicke instead assumes that the term regillam induculam used by Plautus represents a translation of Greek χιτὼν ὀρθοστάδιος (khitṑn orthostádios) (a long ungirded chiton that hung in a straight (ὀρθός (orthós)) line to the ground), and concludes that all subsequent appearances of regillus as a term for a garment in Latin texts (including in Varro) are based on a misunderstanding of the hapax in Plautus.