Big Sister, Elder Sister
Noun
おねえさん
みどりちゃんのお姉さんはめがねをかけています。
Midori’s older sister is wearing glasses.
あなたのこと、てっきりビエトくんのお姉さんだと思ってたんですが、ちがったんですね。
I totally thought you were Viet's older sister, but you aren't, eh?
私のお姉さんは、バイクを買うことが彼氏を見つけることに繋がると考えています。
My older sister thinks that buying a motorcycle will help her get a boyfriend.
The お makes the word more polite. You're elevating the "older sister" title because you're a good younger sibling. Otherwise, the meaning of this word is the same as the kanji - just the feeling is different.
The reading is different too. It has some hiragana attached to it, which is a clue that this uses a kun'yomi reading. Let's use a mnemonic to learn that reading.
Imagine your older sister (even if you don't have one). She is, for some reason, a horse. Imagine petting her, giving her carrots, and doing other horse-related things with her. What do horses say? They say nehhhh (ねえ).