The Etymology of Latin lībra

A common system of measurement terms was a feature of the Italic cultural koiné, which extended from Central Italy to Sicily. The origin of the names of measurement terms, most notably, the unit (Lat. lībra Gk. λίτρα) and its duodecimal subdivision (Lat. uncia, Gk. ὀγκία) have been variously seen as Latin, Greek, or Sicel. In fact, by paying careful attention to the date of attestation and the relative and absolute chronology of sound changes, one can show that uncia cannot be of Latin or Sicel origin, but instead is a specifically Siciliote Greek form derived from Gk. ὄγκος ‘mass, volume’. The unit lībra, on the other hand, must be of Italic origin because the correspondence -b- ~ -t-, as has long been seen, points to divergent reflexes of a PIE voiced aspirate *d^h. The Greek spelling λίτρα with ι resolves another uncertainty: this spelling tells us that the long vowel of Latin is not the result of monophthongization but must continue a Proto-Italic long vowel, in PIE terms *ih_x. We may therefore confidently reconstruct a Proto-Italic *līdhrā. Such a form is amenable to two theoretical morphological analyses. It may either be from a root *(h_x)lei̯h_xd^h- with the suffix *-rā- (< *reh₂), or from a root *(h_x)lei̯h_x- with the instrument suffix *-d^hrā (*-dhreh₂). There are no known roots of the first shape at all, but there are several candidates of the second shape. The root *leih₂- ‘disappear’ seems semantically a non-starter (though it has been suggested), but the root *leih_x- ‘pour’ deserved further consideration. One of the striking features of the Italic measurement system is that the terms are cross-categorical, applying to mass, volume, and even area. Thus lībra and λίτρα are both measures of weight, and volume and the weight meaning in Latin is often specified by pondo (Var. L. 5.182 libram pondo as ualebat “An as was equal to a libra in weight.”) This raises the possibility that lībra was not originally a measure for weight but for volume, as is likely also the case for uncia. We propose therefore that Proto-Italic *līdhrā derives from *lih_xdhreh₂ ‘instrument for pouring’, i.e. a vessel of some sort which was taken to be the standard size for liquid or pourable measure. The root *leih_x- ‘pour’ is unambiguously attested in Lith. líeti ‘to pour (water, etc.), lýti ‘to pour (of rain), OCS lijati ‘to pour’, MW dyllydd ‘flow’ and possibly in extended form in Gk. λείβω, (and Lat. lībāre if not a loanword) < *lei̯h_x-b-.