Television broadcasts of last February's political upheaval in Egypt were regularly interspersed with scenes of the pyramids at Giza. Seeing them, I was reminded that the word for pyramid in Japanese is 金字塔 (kinjitō, "a tower in the shape of the character kin [金]"). (Note the similarity, if you will.)
Usually read as kin, or kane, this character can invoke confusion at times because of the wide variety of meanings ascribed to it. It can refer to metal, specifically gold, but can also be used to refer to money, including paper money, and any type of metal in general. The word for Friday, 金曜日 (kinyōbi), is based on the 五行 (gogyō, five elements) of ancient Chinese cosmology, which are 火 (ka, fire), 土（do, earth), 金 (kin, metal) 水 (sui, water) and 木 (moku, wood). The same character is also used to write the common Korean surname Kim.
As a classifier for other kanji, kin usually appears on the left side, and is called kane-hen. It can be found in many words, including 釘 (kugi, nail), 鎧 (yoroi, armor), 銀（gin, silver), 鈴 (suzu, tin) and 鉛 (namari, lead).