How does the Thorndike-Barnhart pronunciation key indicate a short vowel sound?

The Thorndike-Barnhart pronunciation key uses boldface type to indicate short vowel sounds.

For example:

* a as in cat

* e as in pet

* i as in sit

* o as in hot

* u as in cup

This contrasts with long vowel sounds, which are represented in regular type.

For example:

* a as in ate

* e as in be

* i as in pie

* o as in go

* u as in cube

Therefore, if you see a vowel in boldface, it indicates a short vowel sound.