Focusing on the lack of fingers:
* Glove: This is the most common antonym, as it refers to a covering for the hand with individual sections for each finger.
* Fingered glove: This emphasizes the distinct fingers.
Focusing on the type of covering:
* Bare: This refers to the absence of any covering, meaning the hand is exposed.
* Uncovered: Similar to "bare," this emphasizes the lack of a covering.
Focusing on the purpose:
* Bare hand: This highlights the absence of any tool or protection.
* Tool: This contrasts with the mitten's purpose of warmth or protection.
The best antonym for "mitten" will depend on the context of your sentence.