germanium: a brittle grey crystalline element that is a semiconducting metalloid (resembling silicon) used in transistors; occurs in germanite and argyrodite
chemical element: any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
rappel: (mountaineering) a descent of a vertical cliff or wall made by using a doubled rope that is fixed to a higher point and wrapped around the body