What’s the Plural of Radius? Radii, Radiuses?
The plural of radius is radii or radiuses. Radius is singular.
Grammarflex » plural-nouns » Page 5
Nouns mention people, places, things or ideas. Most nouns are countable, and come in a singular or plural noun form. By and large, most nouns in English add “es” or “s” to denote a plural. These are called “regular nouns”.
Irregular nouns become plural by some other inflection, or they may simply remain as is. These nouns are harder to learn, but we have the answers to all the common questions on proper noun forms; like, “what’s the plural of sheep?”, “is fish plural or singular?”, “is ox plural oxes, or oxen?” To all of your questions on plural nouns, we have the answers. Also, no, meese is not the plural of moose; it’s just moose.
The plural of radius is radii or radiuses. Radius is singular.
Stimulus, like other Latin nouns that have made it to Modern English (syllabus, locus, focus, radius,) uses -I as a plural noun, stimuli.
Criteria, which are a “standard or principle by which something is judged”, is a plural noun. Criterion is the singular of criteria.
Media (pl. n.) singular is medium, in most cases. Media can be used as a mass noun, or non-count noun, which only use singular noun forms.
Apex meaning, “the tip, point, or summit”, comes from Latin; originally, its plural is apices. Apexes has come to be accepted over time.
Just like salmon, tuna and cod, trout stays the same in both the singular and plural case.
Appendixes is the plural of appendix when referring to anatomy. Appendices is plural in reference to a book or document.
Elk (not to be confused with moose and deer, though they all belong to the same Cervid family) is elk or elks, as a plural noun.
The plural of index (a Latin noun) is indexes or indices, though indices is the original, Latin plural form.
Singular nouns that end in -o (like mango) normally add s/es to show a plural, like mangos or mangoes.