Noun plurals (final -f, -fe)

Some nouns drop –f, -fe and add –ves

knife – knives
life – lives
wife - wives

loaf – loaves
shelf – shelves
self – selves
half – halves
thief – thieves
wolf – wolves
calf – calves
leaf – leaves
scarf – scarves

Noun plurals (final -o)

photo - photos
kilo – kilos
piano – pianos
radio – radios
zoo – zoos
Eskimo – Eskimos

tomato – tomatoes
hero – heroes
volcano – volcanoes
mosquito –mosquitoes

zero – zeros / zeroes

Prepositions

Plurals (nouns of foreign origin)

Singular - Plural

cactus-cacti
fungus – fungi / funguses
radius – radii
stimulus – stimuli

axis-axes
analysis – analyses
basis – bases
crisis – crises
diagnosis – diagnoses
hypothesis – hypotheses
oasis – oases
thesis – theses

bacterium – bacteria
criterion – criteria
curriculum – curricula / curriculums
datum – data
medium – media
phenomenon – phenomena
antenna – antennae
formula – formulae / formulas

Irregular plurals

Singular - Plural

woman – women
man – men
child – children
ox – oxen

foot – feet
tooth-teeth
goose – geese

mouse – mice

fish – fish
deer – deer
offspring – offspring
sheep – sheep
species – species
aircraft - aircraft

Past form 'ought' (spelling)

The following verbs have irregular past forms with 'ought'

bring - brought
buy - bought
fight - fought
seek - sought
think - thought

The past tense of 'catch' and 'teach' is spelt differently but has the same sound.
catch - caught
teach - taught

Prefix 'in'

You may change the meaning of some words by adding the prefix ‘in’ (meaning “not”).

inaccurate, inadequate, inadvisable, inappropriate, inauthentic, incapable, incompatible, inconclusive, inconstant, incorrect, incurable, inconvenient, incomplete, inexperienced, independent, indecent, indecisive, indescribable, indestructible, indirect, inefficient, inequality, inessential, inexact, inexcusable, inexpensive, inflexible, infrequent, inhumane, insane, inseparable, insensitive, insignificant