| acrópole | acropolis |
| Acrópole de Atenas | Acropolis of Athens |
| acróstico | acrostic |
| acrômio | acromion |
| acrônimo | acronym |
| Acta de Chapultepec | Inter-American Treaty of Reciprocal Assistance |
| Actaea | Actaea |
| actante | actant |
| actema | acteme |
| Actenoides concretus | Rufous-collared Kingfisher |
| Actenoides hombroni | Blue-capped Kingfisher |
| Actenoides lindsayi | Spotted Kingfisher |
| Actenoides monachus | Green-backed Kingfisher |
| Acteon | Actaeon |
| actigrafia | actigraphy |
| actina | actin |
| actinicamente | actinically |
| Actinidia | Actinidia |
| Actinidia chinensis | Actinidia chinensis |
| Actinidiaceae | Actinidiaceae |
| actinidina | actinidin |
| actinina | actinin |
| actinismo | actinism |
| actino- | actino- |
| actinobacilose | actinobacillosis |
| Actinobacteria | Actinobacteria |
| actinobactéria | actinobacterium |
| Actinocladum | Actinocladum verticillatum |
| actinolita | actinolite |
| actinolite | actinolite |
| actinolito | actinolite |
| actinologia | actinology |
| actinolítico | actinolitic |
| actinometria | actinometry |
| actinomiceta | actinomycete |
| actinomicina | actinomycin |
| actinomicose | actinomycosis |
| actinomicótico | actinomycotic |
| actinomorfo | actinomorphic |
| actinométrico | actinometric |
| Actinopterygii | Actinopterygii |
| actinopterígio | actinopterygian |
| actinorriza | actinorhiza |
| actinostelo | actinostele |
| actinostélico | actinostelic |
| actinoterapia | actinotherapy |
| actinídeos | actinide |
| Actinídio | Actinide |
| actinógrafo | actinograph |
| actinómetro | actinometer |
| actinômetro | actinometer |
| Action Française | Action Française |
| ActionScript | ActionScript |
| Active Directory | Active directory |
| Active Virus Shield | AOL Active Virus Shield |
| ActiveX | Component Object Model |
| Actividade | Buoyancy |
| actividade sísmica | seismic activity |
| actividades antrópicas | anthropic activity |
| actividades de produção | manufacturing activity |
| actividades económicas | economic activity |
| actividades empresariais | business activity |
| actividades industriais | industrial activity |
| actividades institucionais | institutional activity |
| actividades militares | military activities |
| actividades recreativas | leisure activity |
| actividades recreativas locais | local recreation |
| actividades sísmicas | seismic activity |
| actividades terrestres | land-based activity |
| activina | activin |
| Activismo pedófilo | Pro-pedophile activism |
| activista | activist |
| activo fixo | fixed asset |
| acto de fumar | smoking |
| Acto de União | Act of Union |
| Acto falho | Freudian slip |
| acto legislativo | act |
| Acto Único Europeu | Single European Act |
| actomiosina | actomyosin |
| Actor | Actor |
| actos comunitários | Community act |
| actos ilícitos | wrongful act |
| actos jurídicos | juridical act |
| actos legislativos | act |
| ActRaiser | ActRaiser |
| actriz | actor |
| Actróide | Actroid |
| Actualidade | Current affairs |
| Actualmente | Moment |
| Actuação | Game |
| actuário | actuary |
| actígrafo | actigraph |
| actínia | actinia |
| actínico | actinic |
| actínido | actinide |
| actínio | actinium |
| Acube | Akkub |
| acuidade | acuteness |
| acuidade auditiva | hearing acuity |
| acuidadeo | sharpnesss |
| aculeado | aculeate |
| aculeiforme | aculeiform |
| Aculeola nigra | Hooktooth dogfish |
| aculeolado | aculeolate |
| aculturacional | acculturational |
| acultural | acultural |
| aculturalmente | aculturally |
| aculturante | acculturative |
| aculturar | acculture |
| aculturativo | acculturative |
| acumbente | accumbent |
| acume | acumen |
| acumetria | acoumetry |
| acuminado | acuminate |
| Acuminite | Acuminite |
| acumulado | accumulated |
| acumulador | battery |
| acumuladores | accumulator |
| acumular | pile up |
| acumular-se | drift |
