The prefix bi- means “two” or “twice.” Biweekly means either “twice a week” or “every two weeks,” depending on the context.

Anti- means “against” or “opposed to.” Antibiotic refers to something that works against bacteria.

The prefix inter- means “between” or “among.” International describes something that exists or happens “between” nations.

The prefix mis- typically means “wrongly” or “incorrectly.” Misunderstand means “to understand incorrectly.”

The prefix sub- means “under” or “below.” A submarine operates “under” the water.

The prefix re- often means “again.” Redo means “to do again.”

Trans- means “across” or “beyond.” Transport means “to carry across” from one place to another.

The prefix dis- usually means “the opposite of” or “not.” Disagree means “not agree.”

The prefix un- generally means “not” or “the opposite of.” For example, unhappy means “not happy.”

Pre- usually means “before.” Preview means “to view something before” it is officially shown.