函

Glyph origin
Originally, a – an upside-down arrow stored inside a box with one or two handles.

Definitions

 * 1)  to include
 * 2)  box
 * 3)  letter

Kanji

 * 1) a box-shaped receptacle, e.g. a coin bank or letter box (e.g., )
 * 2) to insert [into a container] (cf., )
 * 3) a suit of armor (more commonly )

Etymology
From.