1. Not capable of undergoing fission

Antonym: fissionable

• overpopulation
• overpower
• overpowering
• overpoweringly
• overpraise
• overpressure
• overprice
• overpriced
• overprint
• overproduce
• overproduction
• overproof
• overprotect
• overprotection
• overprotective
• overproud
• overqualified
• overrate
• overrating
• overreach
• overreaching
• overreact
• overreaction
• overreckoning
• overrefine