Mates

The Chinese, as well as other "rújiā wénhuà" 儒家文化 ("Confucian cultures"), are very conscious of the types of relationships between people. Here are some of those "chēnghū" 称呼 ("terms of address") that they use all the time. I've come across all of these in daily conversation.NOTE: all of these can be used to fill in the blank when introducing someone as follows:tā shì wǒ de _________ 他是我的 = he is my ________

At school

• tóngzhuō 同桌 = desk-mate, seat-mate
• tóngchuāng(hǎoyǒu) 同窗(好友) = close friend
• shìyǒu 室友 = roommate
• tóngxué 同学 = classmate (same study program)
• tóngbān 同班 = classmate (exact same class)
• xiàoyǒu 校友 = schoolmate

Graduate Students

All of the following have to do with graduate students and their "dǎoshī" 导师 ("academic adviser/teacher"). These terms apparently date back to "gōngfu" 功夫 ("kung fu") masters and their students. If the student had been studying gongfu longer, they were referred to with the older brother/sister words, and vice versa. In English we really don't have translations for these. So, for convenience, I've coined the term "adviser-mate."

• tóngmén 同门 = have/had the same academic adviser ("adviser-mate")
• shījiě 师姐 = "adviser-mate" (studied longer, girl)
• shīxiōng 师兄 = shīgē 师哥 = "adviser-mate" (studied longer, boy)
• shīmèi 师妹 = "adviser-mate" (studied shorter, girl)
• shīdì 师弟 = "adviser-mate" (studied shorter, boy)

NOTE: tóngmén 同门 is the generic term and can be used independently or in conjunction with the other 4 like this: tóngménshījiě 同门师姐

Anywhere

• tóngshì 同事 = colleague, coworker
• lǎoxiāng 老乡 = someone from the same hometown
• tóngchuáng 同床 = bedfellow, bedmate

Friends

• mìyǒu 密友 = close friend
• lǎo péngyou 老朋友 = old friend
• hǎo péngyou 好朋友 = good friend

This doesn't include the huge manifest of family relationships (see also Chinese Family Tree, Terms of Endearment, and Addressing Strangers).If anyone knows of any more of these relationship kinds of words, please feel free to leave them in a comment.