| | Lladin |
| abacus (eg) | abacus | |
| absisa | abscissa | |
| absoliwt | absolute | |
| absorb | amsugno | |
| achromatig | achromatic | |
| acnod | acnode | |
| acwsteg | acoustics | |
| acwstig | acoustic | |
| acwsto-opteg (eb) | acousto-optics | |
| adain ariannaidd
(eb) | Grey Shoulder-knot
| Lithophane ornitopus
|
| adain brin
(eb) | Nonconformist
| Lithophane lambda
|
| adain ddeifiog
(eb) | Scorched Wing
| Plagodis dolabraria
|
| adain ddu
(eb) | Chimney Sweep
| Odezia atrata
|
| adain Gymreig
(eb) | Conformist
| Lithophane furcifera
|
| adain hirgron
(eb) | Horse Chestnut
| Pachycnemia hippocastanaria
|
| adain lwydfelen
(eb) | Tawny Pinion
| Lithophane semibrunnea
|
| adain welw
(eb) | Pale Pinion
| Lithophane hepatica
|
| adeiniog | spoked | |
| adend | addend | |
| aderyn drycin bach (eg) | little shearwater
| Puffinus assimilis
|
| aderyn drycin Cory (eg) | Cory's shearwater
| Calonectis diomedea
|
| aderyn drycin du (eg) | sooty shearwater
| Procellaria griseus
|
| aderyn drycin Manaw (eg) | Manx shearwater
| Puffinus puffinus
|
| aderyn drycin mawr (eg) | great shearwater
| Puffinus gravis
|
| aderyn drycin y graig (eg) | fulmar
| Fulmarus glacialis
|
| aderyn y bwn (eg) | bittern
| Botaurus stellaris
|
| aderyn y bwn America (eg) | American bittern
| Botaurus lentiginosus
|
| aderyn y bwn lleiaf (eg) | little bittern
| Ixobrychus minutus
|
| aderyn y to (eg) | house sparrow
| Passer domesticus
|
| adiabatig | adiabatic | |
| adio | add | |
| adiol | additive | |
| adlewyrchydd | reflector | |
| adlyniad | adhesion | |
| adsugniad | adsorption | |
| adsugno | adsorb | |
| adweithydd | reactant | |
| agorfa | aperture | |
| agrecanas (eg) | aggrecanase | |
| alarch Bewick (eg) | Bewick's swan
| Cygnus bewickii
|
| alarch dof (eg) | mute swan
| Cygnus olor
|
| alarch y Gogledd (eg) | whooper swan
| Cygnus cygnus
|
| Alban Arthan | winter solstice | |
| Alban Hefin | summer solstice | |
| albatros aelddu (eg) | black-browed albatross
| Diomedea melanophris
|
| alcali | alkali | |
| aloi | alloy | |
| alotropaidd | allotropic | |
| alotropi | allotropy | |
| amgrwm | convex | |
|
|