Contronyms are words that are their own antonymns.

sanction means to approve (the governor will sanction the organization)
sanction means to penalize (the trade sanction prevented export)

screen means to show information (the movie will screen Thursday)
screen means to hide information from viewing (the warden will screen the mail)

seed means to plant an area with seed (seed the future lawn)
seed means to remove seeds from something (seed a tomato)