ex

"ex" takes the ABLATIVE and means "out of", from inside something: out of a city, out of a group, out of a period of time. Its sibling "ab" means "away from" the outside of a thing, and "de" means "down from", so the three carve up motion away between them rather than overlapping.

The short form "e" is the same word. Romans wrote "ex" before a vowel and either form before a consonant, so "e navi" and "ex navi" are both correct. The partitive use is worth memorising as a phrase: "unus ex militibus" is how Latin usually says "one of the soldiers", in preference to a genitive.