1. The correspondent part; a copy; a duplicate; the part which fits another, as the key of a cipher; the complementary part; the part to be applied to another.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• counterpats,
• counterpaerts,
• counterpars,
• counterfait,
• conunterpart,
• couterpart,
• conterparts,
• cunterparts,
• counteparts,
• conterpart,
• counterparty,
• counterpace,
• counterirrittant,
• countermarc,
• counterpary,
• couinterpart,
• counterparet,
• counterparrt,
• counerpart,
• countrpart

• counterman,
• counterculture,
• countermelody,
• counter-drill,
• contrite,
• counteractive,
• counter check,
• Conteras,
• counterblast,
• counter tube,
• counterstrike,
• commuter,
• countersink,
• countertop,
• countermarch,
• counterplay,
• counterwoman,
• counterfire,
• countercoup,
• counterglow,
• countertenor,
• counterplea,
• counterblow,
• counterfactual,
• counterperson,
• counterclaim,
• counterpane,
• countersuit,
• counterweight,
• counterplan,
• countervail,
• counterpoint,
• countersign,
• countercharge,
• counterpoison,
• counterpoise,
• connatural,
• Contreras,
• counterstain,
• counterfeiter,
• counterspy,
• counterpoised,
• counterfeit,
• countercheck,
• counterchange,
• counteroffer,
• counterpose,
• counterplot,
• countermand,
• counteract,
• counterattack,
• counterbore,
• counterpunch,
• countercurrent,
• counterfoil,
• counterexample,
• countershot,
• conterminous,
• countermove,
• counteraction,
• countermine.

The adverb form of the word "counterpart" is "counterpartly".

The adjective form of the word "counterpart" is "counterparted". However, it is not commonly used in English.

The plural of the "counterpart" can be the "counterparts".

The singular of the "counterpart" can be the "counterpart".