| act big | actuar jactanciosamente |
| act boastfully | actuar jactanciosamente |
| act for | representar |
| act haughty towards | condescender |
| act in opposition to | oponerse a |
| act in place of | versar |
| Act in the law | Negocio jurídico |
| Act like a child | Hacer chiquilinadas |
| Act of Accord | Acta de Acuerdo |
| act of God | fuerza mayor |
| Act of Independence of Lithuania | Declaración de Independencia de Lituania |
| Act of oblivion | Amnistía |
| Act of Parliament | Derecho |
| Act of Union | Acta de Unión |
| act on one's own discretion | al albedrío de uno |
| act uppity towards | condescender |
| Acta Diurna | Acta Diurna |
| Acta Sanctorum | Actas de los santos |
| actability | viabilidad |
| Actaea | Actaea |
| Actaea spicata | Actaea spicata |
| Actaeon | Acteón |
| Actaeus | Acteo |
| Acteal massacre | Matanza de Acteal |
| Actias selene | Actias selene |
| actin | actina |
| acting | acción |
| Acting minister | Interinato |
| actinic | actínico |
| actinide | actínido |
| Actinidia | Actinidia deliciosa |
| Actinidia chinensis | Actinidia deliciosa |
| Actinidia deliciosa | Actinidia deliciosa |
| Actinidiaceae | Actinidiaceae |
| actinism | actinismo |
| Actinium | Actinio |
| Actinobacteria | Actinobacteria |
| Actinocladum verticillatum | Actinocladum |
| actinometer | actinómetro |
| actinometric | actinométrico |
| Actinomyces | Actinobacteria |
| Actinomycetaceae | Actinomycetaceae |
| actinomycosis | actinomicosis |
| Actinopterygii | Actinopterygii |
| action | acción |
| Action Against Hunger | Acción Contra el Hambre |
| action committee | grupo de acción |
| Action directe | Acción Directa |
| Action démocratique du Québec | Acción Democrática de Quebec |
| Action Française | Action Française |
| action group | grupo de acción |
| Action of force | Agresión |
| Action role-playing game | ARPG |
| actionable | procesable |
| actions speak louder than words | obras son amores, que no buenas razones |
| ActionScript | ActionScript |
| Actis | Actis |
| activate | activar |
| activated carbon | carbón activado |
| Activated complex | Complejo activado |
| activated sludge | lodos activados |
| activation | activación |
| activator | activador |
| active | enérgico |
| Active directory | Active Directory |
| Active galactic nuclei | Núcleo activo de galaxia |
| Active galaxy | Galaxia activa |
| Active imagination | Imaginación activa |
| active ingredient | principio activo |
| Active layer | Mollisol |
| active matrix | matriz activa |
| Active optics | Óptica activa |
| active participation | participación activa |
| Active pixel sensor | Sensor CMOS |
| active population | población activa |
| Active record pattern | Patrón ActiveRecord |
| Active Server Pages | Active Server Pages |
| Active site | Sitio activo |
| Active sun | Sol activo |
| Active transport | Exocitosis |
| active voice | voz activa |
| active volcano | volcán |
| actively | enérgicamente |
| activeness | actividad |
| ActiveX Data Objects | ActiveX Data Objects |
| activism | activismo |
| activist | activista |
| activity | acción |
| Activity index | Índice de actividad |
| actor | actor |
