| Across-the-board | General |
| acrostic | acróstico |
| acrostical | acróstico |
| Acrotatus | Acrótato |
| Acryl group | Polimetilmetacrilato |
| acrylamide | acrilamida |
| acrylate | acrilato |
| acrylic | acrílico |
| acrylic acid | ácido acrílico |
| acrylonitrile | acrilonitrilo |
| Acrylonitrile butadiene styrene | Acrilonitrilo butadieno estireno |
| act | acción |
| Act alone | Caballero |
| act as | servir como |
| act before | actuar antes |
| 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 |
