| diagnosis | diagnoses |
| bacterium | bacteria |
| basis | bases |
| cactus | cacti |
| concerto | concertos |
| diagnosis | diagnoses |
| echo | echoes |
| fish | fish |
| formula | formulae/s |
| goose | geese |
| half | halves |
| index | indices |
| larva | larvae |
| lay-by | lay-bys |
| leaf | leaves |
| lens | lenses |
| loaf | loaves |
| penny | pence |
| salmon | salmon |
| series | series |
| sheep | sheep |
| stimulus | stimuli |
| ultimatum | ultimata |
| louse | lice |
| oasis | oases |
| criterion | criteria |
| phenomenon | phenomena |
| syllabus | syllabi |
| aircraft | aircraft |
| carp | carp |
| crossroads | crossroads |
| deer | deer |
| means | means |
| pike | pike |
| species | species |
| trout | trout |