Type Singular Plural Origin Examples in Use
Latin: -us → -i alumnus alumni Latin He is a respected alumnus of Harvard.
radius radii The radii of the circle are equal.
Latin: -um → -a curriculum curricula Latin The school offers varied curricula.
datum data All data have been analyzed.
Latin: -a → -ae formula formulae / formulas Latin The formulae were derived from theory.
Greek: -is → -es analysis analyses Greek Her analyses were spot on.
crisis crises Several crises emerged simultaneously.
Latin: -ex/-ix → -ices index indices / indexes Latin The book has two useful indexes.
appendix appendices Read the appendices for details.
Greek: -on → -a phenomenon phenomena Greek These are rare phenomena.
criterion criteria Each criterion must be met.
Pluralia Tantum — scissors English/Latin The scissors are sharp.
— clothes All her clothes were new.
— cattle The cattle are grazing.
Singularia Tantum news — English The news is shocking.
furniture — The furniture needs dusting.
luggage — Her luggage was lost.