- that measures two inches by four inches, two feet by four feet, etc.
- Informal small, narrow, cramped, etc.
- Measuring two units by four units, especially inches.
- Slang Small in size; boxed in or cramped: a two-by-four apartment.
- A length of timber having this cross section. (Note: often this is dimensional lumber that was this size BEFORE being planed to finished form, which removes a quarter inch from each side.)