(construction) A length of lumber having a cross section of two inches by four inches, or in the case of dimensional lumber three and a half inches by one and a half inches.

Consisting of two layers or two strands. / (textile fabrics) Consisting of two webs woven into one another. / (manufactured articles, linen) Consisting of two thicknesses.

Having two colours or shades. / Giving two different sounds, either alternately or simultaneously.

(US, informal) costing 25 cents / (US, idiomatic, slang) insignificant or worthless

comprising two pieces

A garment consisting of two separate parts; especially such a swimsuit

Having two sides, bilateral. / Reversible. / (algebra) Whose salient properties apply when (the specified object) appears on either side of a given binary operator.

A vehicle with seats for two people (a driver or pilot and one passenger)

Using both fists (or, figuratively, hands). / (informal) Energetic, enthusiastic. / Inclined to fight, belligerent

Using or designed for use by both hands at once. / Involving, or designed for use by, two people. / Ambidextrous. / Having two hands. / (UK, slang, dated) Good with one's fists; able to fight well.