oppositeTheir two daughters may look alike, but they are completely opposite to one another.
polar oppositesLove and hate are polar opposites.
identicalHis opinions are identical to his spouse's.
antitheticalformalHis actions were absolutely antithetical to our code of conduct.
converseformalIf we ask what a citizen must sacrifice for the good of the nation, we must ask the converse question: what will the nation sacrifice for the good of its citizens?
be like chalk and cheeseUKHe and his younger brother are like chalk and cheese.