A unit of length, used in astronomy, defined as the distance from the Earth of an object that exhibits a parallax of 1 arcsecond. It is approximately equal to 3.08568025 × 10¹³ kilometers or 3.2616 light years.

(sports) A unit of players which is considered to have a secondary level of talent and which usually plays after the first string.

(idiomatic) Not as good; of a lower quality or condition.

(UK, military, nautical, historical) Of a Royal Navy ship of the line in the Napoleonic Era: having 80–98 guns across three gun decks, a complement of 700–750, and weighing approximately 2,200 tons burthen.

(UK, military, nautical, historical) A second-rate ship of the line.

(UK) Alternative form of on second thought

As good as the best, as in quality or reputation; inferior to no one else or to nothing else of the same kind.

(slang, sometimes capitalized) Heroin.

(cinematography) A separate team that shoots footage that is of secondary importance for the final cut of the motion picture, as opposed to first unit.

Alternative spelling of second half