Q:

Looking for a single word that describes "up to but not including x" where x is a number

Pretty straight forward; I am looking for a word that describes up to, but not including a certain number, if such a word exists.

A:

In most numerical contexts we use "less than". That's two words, not one, but it may work for you. 

A:

Below is an obvious one-word answer (I have to write more 'cos it's below the minimum length!).

A:

"Under", meaning "less than", is only one word. Under X.

