organism (including. but not limited to. weeds. insects. or fungi) that is damaging. noxious. or a nuisance.
Merriam-Webster Online Dictionarypest (noun)
an epidemic disease associated with high mortality , specifically - plague
something resembling a pest in destructiveness , especially a plant or animal detrimental to humans or human concerns (as agriculture or livestock production)
one that or annoys - pesters nuisance