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.
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?
inverseThere is an inverse relationship between the Prime Minister's popularity and the direction of the financial markets.
be like chalk and cheeseUKHe and his younger brother are like chalk and cheese.