The Grammar of English Grammars, page 600 by Gould Brown
<< Return to Title Details & Download601
eed of the plural; as, _bdellium, decorum, elysium, equilibrium, guaiacum, laudanum, odium, opium, petroleum, serum, viaticum_. Some form it regularly; as, _asylums, compendiums, craniums, emporiums, encomiums, forums, frustums, lustrums, mausoleums, museums, pendulums, nostrums, rostrums, residuums, vacuums_. Others take either the English or the Latin plural; as, desideratums or _desiderata, mediums_ or _media, menstruums_ or _menstrua, memorandums_ or _memoranda, spectrums_ or _spectra, speculums_ or _specula, stratums_ or _strata, succedaneums_ or _succedanea, trapeziums_ or _trapezia, vinculums_ or vincula. A few seem to have the Latin plural only: as, _arcanum, arcana; datum, data; effluvium, effluvia; erratum, errata; scholium, scholia_.
3. Of nouns in us, a few have no plural; as, _asparagus, calamus, mucus_. Some have only the Latin plural, which usually changes us to _i_; as, _alumnus, alumni; androgynus, androgyni; calculus, calculi; dracunculus, dracunculi; echinus, echini; magus, magi_. But such as have properly become English words, may form the plural regularly in _es_; as, _chorus, choruses_: so, _apparatus, bolus, callus, circus, fetus, focus, fucus, fungus, hiatus, ignoramus, impetus, incubus, isthmus, nautilus, nucleus, prospectus, rebus, sinus, surplus_. Five of these make the Latin plural like the singular; but the mere English scholar has no occasion to be told which they are. Radius makes the plural radii or radiuses. Genius has genii, for imaginary spirits, and geniuses, for men of wit. Genus, a sort, becomes genera in Latin, and genuses in English. Denarius makes, in the plural, denarii or denariuses.
4. Of nouns in is, some are regular; as, _trellis, trellises_: so, _annolis, butteris, caddis, dervis, iris, marquis, metropolis, portcullis, proboscis_. Some seem to have no need of the plural; as, _ambergris, aqua-fortis, art