altus

Altus, alta, altum, first and second declension, comparative altior, superlative altissimus. It means high and deep at once, which looks like sloppiness and is not: altus is the perfect participle of alo, "I nourish, I grow", so it describes what has grown, measured along its axis without saying which end you are standing at. A wall is altus upwards, a river altus downwards, and only the noun tells you.

The neuter altum used alone is a noun, the open sea, and in altum means out to deep water. Alte as an adverb is "on high" or "deeply". The family gives altitudo, exalto and English altitude, exalt, altar and the musical alto, which was the high voice before it was the low one.