1. Exceedingly harmful
   - baneful, deadly, pernicious 
2. Likely to spread and cause an epidemic disease
   - pestilential, pestiferous, plaguey

See also: epidemic, noxious, pestilence

• apparent movement
• apparently
• apparentness
• apparition
• apparitional
• appeal
• appeal board
• appealable
• appealing
• appealingly
• appealingness
• appeals board
• appeals court
• appear
• appearance
• appearing
• appeasable
• appease
• appeasement
• appeaser
• appeasing
• appellant
• appellate
• appellate court
• appellation