Older Brother
Guy
noun
This word starts with an お to make it more polite. Then it has the kanji 兄 which you already know. Lastly, it has さん which is an honorific to elevate people and be polite. This is basically the formal way of saying older brother (versus plain old 兄). It can also be used to refer to a guy that you don't know who has a youthful appearance.
The reading for this one is pretty tricky, and I'd consider it an exception. To remember it, you have to learn the 兄 part, and everything else will fall into place. Here's a mnemonic to help you:
Your (kind) older brother pushes you down on the ground. You stand up and look at your knee (にい), which is all bloody. "Why'd you do that to my knee!?" you ask. "You're supposed to be a nice older brother, that's why I call you お兄さん!"
お兄さんはやさしい
Older Brother is kind
お兄さんはおもしろい
Older Brother is amusing
お兄さんはこわい
Older Brother is scary
お兄さんのかお
Older Brother's face
お兄さんのビー玉
Older Brother's marble
お兄さんのノート
Older Brother's notes
お兄さんといっしょ
together with Older Brother
お兄さんとお姉さん
Older Brother and Older Sister
お兄さんとあそぶ
to play with Older Brother
大学生のお兄さん
Older Brother who is a university student
花ちゃんのお兄さん
Hana's older brother
友人のお兄さん
a friend's older brother
お兄さんがやる
Older Brother does something
お兄さんがいる
to have an older brother, Older Brother is here
お兄さんがする
Older Brother does something
あの男の人が、山田さんのお兄さんです。
That man is Yamada's older brother.
私のお兄さんは体が大きくて、仕草も男の子らしいです。
My older brother is big and he also has a masculine demeanor.
ちょっと、そこのお兄さん！シャツに血がついてますよ！
Hey there! Your shirt has some blood on it!