The cardinal number occurring after three hundred ninety-nine and before four hundred one, represented in Arabic numerals as 400.

A method of encoding Chinese characters using four numerical digits per character (in some situations, an additional digit is used).

(idiomatic, derogatory) A person who wears spectacles.

(In both the 12-hour clock and the 24-hour clock) The start of the fifth hour of the day; 4:00 a.m. (04:00). / (Only in the 12-hour clock) The start of the seventeenth hour of the day; 4:00 p.m. (16:00).

Acknowledgment of message received.

A sport played by four players where players have to hit a ball into other people's squares, and attempt to make a return hit.

(chiefly Canada, US) A length of sawn wood of cross section approximately 2 inches by 4 inches, most often employed as structural framing lumber (dimension or dimensional lumber).

(Australia, UK, New Zealand) A length of sawn wood of cross section 4 inches by 2 inches, most often employed as structural framing lumber / timber.

(baseball) The sign made by the manager directing the pitcher to issue an intentional walk.

measuring two inches by four inches / (by extension) small or cramped