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