| acta | chart |
| Acta adicional | Additional clause |
| Acta de abjuración | Oath of Abjuration |
| Acta de Acuerdo | Act of Accord |
| Acta de calidad | Quality label |
| Acta de Islas Guaneras | Guano Islands Act |
| Acta de la Norteamérica británica | British North America Acts |
| Acta de Substancias Controladas | Controlled Substances Act |
| Acta de Supremacía | Acts of Supremacy |
| Acta Diurna | Acta Diurna |
| Acta Negra | Black Act |
| Acta notarial | Notarial deed |
| Acta Solemne de la Declaración de Independencia de la América Septentrional | Solemn Act of the Declaration of Independence of Northern America |
| Actaea | Actaea |
| Actaea spicata | Actaea spicata |
| actas | proceedings |
| Actas de los Mártires | Acts of the Martyrs |
| Actas de los santos | Acta Sanctorum |
| Actas de Navegación | Navigation Acts |
| Actas Intolerables | Intolerable Acts |
| Actea | Claudia Acte |
| Acteo | Actaeus |
| Acteón | Actaeon |
| Actias selene | Actias selene |
| actina | actin |
| Actinaria | Sea anemone |
| Actiniaria | Sea anemone |
| Actinidia | Actinidia |
| Actinidia deliciosa | Kiwi |
| Actinidiaceae | Actinidiaceae |
| actinio | actinium |
| actinismo | actinism |
| Actinobacteria | Actinobacteria |
| Actinocladum | Actinocladum verticillatum |
| actinomicosis | actinomycosis |
| Actinomycetaceae | Actinomycetaceae |
| actinométrico | actinometric |
| Actinopterygii | Actinopterygii |
| actinómetro | actinometer |
| Action Française | Action Française |
| ActionScript | ActionScript |
| Actis | Actis |
| actitud | view |
| actitud NIMBY | NIMBY aptitude |
| activación | activation |
| activador | activator |
| activamente | actively |
| activar | activate |
| Active Directory | Active directory |
| Active Server Pages | Active Server Pages |
| ActiveX Data Objects | ActiveX Data Objects |
| actividad | busyness |
| actividad antrópica | anthropic activity |
| actividad bancaria | banking |
| actividad con base en tierra | land-based activity |
| actividad de fabricación | manufacturing activity |
| actividad de la empresa | branch of activity |
| actividad económica | economic activity |
| actividad empresarial | business activity |
| actividad física | physical activity |
| actividad industrial | industrial activity |
| actividad mental | mental activity |
| actividad minera en fondo marino | deep sea mining |
| actividad recreativa | recreation |
| actividad recreativa multitudinaria | mass recreation |
| actividad social | social activity |
| actividad sísmica | seismic activity |
| Actividad óptica | Optical rotation |
