From altum, supine of alō (“grow”). Corresponds to Proto-Italic *altos, from Proto-Indo-European *h₂eltós, a suffixed form of the root *h₂el- (“grow, nourish”) (compare Proto-Germanic *aldaz, whence English old and world).
Ćwicz mówienie i zapamiętywanie " altus " i wielu innych słów i zdań z łaciński .