1. Exceedingly harmful
   - deadly, pernicious, pestilent 
2. Deadly or sinister
   - baleful

See also: maleficent, noxious

• overambitious
• overanxiety
• overanxious
• overappraisal
• overarch
• overarm
• overawe
• overawed
• overbalance
• overbear
• overbearing
• overbearingly
• overbearingness
• overbid
• overbite
• overblown
• overboard
• overboil
• overbold
• overbook
• overbridge
• overbuild
• overburden
• overburdened
• overbusy