The opposite sex — people of a different gender (e.g., friends of the opposite sex).
大学では異性の友達がたくさんできた。
I made a lot of friends of the opposite sex at university.
彼は異性と話すと緊張してしまう。
He gets nervous when talking to members of the opposite sex.
異性との付き合い方について相談に乗る。
I'll give you advice on how to interact with the opposite sex.
異性からの視線を強く感じた。
I strongly felt someone's gaze from the opposite sex.
Isomerism in chemistry — the property of having different structural arrangements or stereochemistry despite the same molecular formula.
この化合物には複数の異性体が存在する。
This compound has several isomers.
立体異性と構造異性は化学で重要な概念だ。
Stereoisomerism and structural isomerism are important concepts in chemistry.