- araneid
- araneose
- Aranha
- Aran Islands
- Aranrhod
- Arany
- Aranyaka
- Arapaho
- Arapahoe
- Arapaho Peak
- arapaima
- Arapesh
- Ararat
- araroba
- Aras
- Aratus of Sicyon
- Araucan
- Araucana
- Araucania
- Araucanian
- araucaria
- Arawak
- Arawakan
- Arawn
- Araxá
- Araxes
- arb
- ARB
- arba kanfoth
- arbalest
- Arbela
- Arber
- Arbil
- arbiter
- arbiter elegantiae
- arbitrable
- arbitrage
- arbitrager
- arbitral
- arbitrament
- arbitrarily
- arbitrariness
- arbitrary
- arbitrate
- arbitration
- Arbitration, The
- arbitration bar
- arbitrator
- arbitrer
- arbitress
- Arblay
- Arblay, d'
- arbor
- arboraceous
- Arbor Day
- arboreal
- arbored
- arboreous
- arborescent
- arboretum
- arboriculture
- arborio
- arborio rice
- arborist
- Arborite
- arborization
- arborous
- arborvitae
- arbor vitae
- arbour
- arbovirus
- Arbroath
- arbtrn.
- Arbus
- arbuscular mycorrhiza
- Arbuthnot
- arbutus
- arc
- ARC
- Arc, d'
- arca
- arcade
- arcaded
- arcade game
- Arcadia
- Arcadian
- Arcadic
- Arcado-Cyprian
- Arcady
- arcana
- arcane
- arcanist
- arcanum
- arcanum arcanorum
- Arcaro
- Arcas
- Arcata
- arcature
- arc-back
- arc-boutant
- arccos
- arc cos
- arc cosecant
- arc cosine
- arc cotangent
- Arc de Triomphe
- Arce
- Arcella
- Arcesilaus
- Arcesius
- arcform
- arc furnace
- arch
- arch-
- arch.
- Arch.
- Arch. E.
- archaea
- Archaea
- archaean
- Archaean
- archaebacteria
- archaebacterium
- archaeo-
- archaeoastronomy
- archaeobotany
- Archaeocyathid
- archaeol.
- archaeological
- archaeologist
- archaeology
- archaeomagnetism
- archaeomagnetism dating
- archaeometry
- archaeon
- archaeopteryx
- archaeornis
- Archaeozoic
- archaezoology
- archaic
- archaic Homo
- archaic Homo sapiens
- archaic smile
- archaism
- archaize
- archangel
- Archangel
- arch beam
- archbishop
- archbishopric
- arch board
- Archbp
- Archbp.
- arch brace
- archconfraternity
- archconservative
- archd.
- Archd.
- arch dam
- archdeacon
- archdeaconry
- archdiocese
- archducal
- archduchess
- archduchy
- archduke
- archdukedom
- arche-
- Archean
- archebanc
- arched
- arched squall
- arched truss
- archegoniophore
- archegonium
- archencephalon
- archenemy
- archenteron
- archeo-
- archeoastronomy
- archeocyte
- archeology
- archeometry
- Archeozoic
- Archeptolemus
- archer
- Archer
- archerfish
- archery
- Arches
- Arches National Park
- archespore
- archesporium
- archetto
- archetypal
- archetype
- archfiend
- arch head
- archi-
- Archibald
- Archibald prize
- archibenthos
- archiblast
- archiblastic
- archicarp
- archidiaconal
- archidiaconate
- Archie
- Archie Bunker
- archiepiscopacy
- archiepiscopal
- archiepiscopate
- archil
- Archilochian
- Archilochus
- archimage
- archimandrite
- Archimedean
- Archimedean solid
- Archimedes
- Archimedes' principle
- Archimedes' screw
- archine
- arching
- archipelago
- Archipenko
- archiphoneme
- archiplasm
- archit.
- architect
- architectonic
- architectonics
- architectural
- architectural bronze
- architecture
- architecture parlante
- architrave
- archival
- archival storage
- archive
- archivist
- archivolt
- archliberal
- archlute
- archly
- archness
- archon
- archoplasm
- archosaur
- archpriest
- archrival
- archsee
- arch support
- archt.
- archway
- Archy
- arciform
- Arcimboldi
- Arcimboldo
- arcing
- Arciniegas
- arc-jet engine
- arcked
- arc lamp
- arc light
- ARCM
- arcmin
- arco
- Arc of Lowitz
- arcograph
- arcology
- arcosolium
- ARCS
- arcsec
- arc sec
- arc secant
- arc second
- arcsin
- arc sine
- arc spectrum
- arctan
- arc tan
- arc tangent
- arctic
- Arctic
- arctic char
- Arctic char
- Arctic Circle
- Arctic daisy
- arctic fox
- Arctic fox
- arctic hare
- Arctic Monkeys
- Arctic Ocean
- Arcticologist
- Arcticology
- Arctic Red River
- Arctic seal
- Arctic Stream
- arctic tern
