What is the schwa vowel in cactus?

The schwa vowel in "cactus" is the ə sound in the first syllable.

Here's the breakdown:

* ˈkak.təs

* ˈ indicates the stressed syllable

* ə represents the schwa sound

The schwa sound is a very short, unstressed vowel sound, often described as a "uh" sound. In "cactus," the schwa sound is very subtle and almost disappears.