Why does LAX have an X?

Los Angeles is LAX and Portland, Oregon is PDX. In both cases, the X doesn't stand for anything.

From two letters to three

In the early days of US aviation, many airports used two-letter codes, borrowed from the weather service. Los Angeles was LA and Portland was PD. When three-letter codes became the standard, some airports simply kept their old two letters and added an X to fill the gap.

Does X mean anything else?

Not by itself. Plenty of codes contain an X for other reasons, such as KIX for Osaka's Kansai International. If you're guessing, an X at the end of a US code is often a sign of this old two-letter history.

Try it yourself

Next time you see a code ending in X, check whether the first two letters make sense on their own. For LA and PD, they do.