tardus.

From Proto-Italic *tardo-, from Proto-Indo-European *tr̥h₂-d-o-, from the root *terh₂- (“to cross over, pass through, overcome”). The phonetic development follows the regular Latin outcome of a syllabic liquid followed by a laryngeal (*r̥h₂ > -ar-). Semantically, the word likely shifted from "drawn out" or "taking a long time to cross/endure" to "slow" or "late". Cognate with Sanskrit तरति (tárati, “crosses over, overcomes”) and Ancient Greek τρανής (tranḗs, “piercing, clear, distinct”). While this is the standard Indo-European reconstruction, De Vaan notes the etymology remains "uncertain" due to the lack of direct cognates with the specific meaning of "slow" in other branches, and an Etruscan origin has occasionally been suggested.