re is
another vowel in the syllable; as, key, keys; delay, delays;
attorney, attorneys; valley, valleys; chimney, chimneys.

6. _Mathematics, metaphysics, politics, optics, ethics, pneumatics,
hydraulics_, &c. are construed either as singular or plural nouns.

7. The word _news_ is always singular. The nouns _means, alms_, and
_amends_, though plural in form, may be either singular or plural in
signification. Antipodes, credenda, literati, and minutiae are
always plural. _Bandit_ is now used as the singular of Banditti.

8. The following nouns form their plurals not according to any
general rule; thus, man, men; woman, women; child, children; ox,
oxen; tooth, teeth; goose, geese; foot, feet; mouse, mice; louse,
lice; brother, brothers or brethren; cow, cows or kine; penny,
pence, or pennies when the coin is meant; die, dice _for play,_
dies _for coining;_ pea and fish, pease and fish when the species
is meant, but _peas_ and _fishes_ when we refer to the number; as,
six _peas_, ten _fishes_.

9. The following compounds form their plurals thus: handful,
handfuls; cupful, cupfuls; spoonful, spoonfuls:--brother-in-law,
brothers-in-law; court-martial, courts-martial.

The following words form their plurals according to the rules of the
languages from which they are adopted.

_Singular_ _Plural._
Antithesis antitheses
Apex apices
Appendix appendixes _or_ appendices
Arcanum arcana
Automaton automata
Axis axes
Basis bases
Beau beaux _or_ beaus
Calx calces _or_ calxes
Cherub cherubim _or_ cherubs
Crisis crises
Criterion criteria
Datum data
Diaeresis diaereses
Desideratum desiderata
Effluvium effluvia
Ellipsis ellipses
Emphasis emphases
Encomium encomia _or_ encomiums
Erratum errata
Genius genii [2]
Genus genera
Hypothesis hypotheses
Ignis fatuus, ignes fatui
Index indices _or_ indexes [3]
Lamina laminae
Magus magi
Memorandum memoranda _or_ memorandums
Metamorphosis