In German, alt means old, so, for example, altschuler means old school.
In usenet, alt means alternate.
In US English, alt means high or deep, as in altimeter.
On a keyboard, alt means hold down the ALT key while pressing another key.
There are probably many more meanings of the prefix alt.
prefix
High, deep.
The prefix "alt" typically means alternative or alternate. It is used to indicate a different or substitute option, as in words like "alternative," "alternate," or "altercation."
One who lusts., Alt. of Lustre, Alt. of Lustre
what is the prefix meaning of in
The prefix "acro-" conveys the meaning of height.
Alt. of Confidante
Alt. of Boulder
prefix
The prefix "out" typically denotes something that is beyond or outside of a place or condition. It can indicate removal, exclusion, or completion of an action.
prefix meaning fast
The prefix meaning "billion" is "giga-".