(boxing) A combination of two punches, one from each hand, thrown in rapid succession. / (by extension) A rapid sequence or combination of two things that has a quick or powerful effect.

plural of two-seam fastball

(transport, idiomatic) A rule of thumb for safe driving by which a driver must maintain a two-second distance from the vehicle in front.

plural of two-way mirror

A mirror that is partially reflective and partially transparent

(idiomatic) Two equivalent choices or situations.

(algebra) A subring which is both a left ideal and a right ideal. Commonly referred to simply as an ideal, but referred to as two-sided ideal for emphasis.

plural of one-two punch

a rule of thumb by which a driver may maintain a safe following distance, allowing at least a two second interval behind any vehicle that is directly in front of the driver's vehicle.

Indicates the speaker wishes to buy two beers.