from The American Heritage® Dictionary of the English Language, 4th Edition
- n. One who is habitually doubtful.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One who requires proof before believing.
- n. One who finds belief difficult.
After Saint Thomas, who doubted Jesus's resurrection until he had proof of it.(American Heritage® Dictionary of the English Language, Fourth Edition)
Eponym for the Apostle Thomas. (Wiktionary)