les: _alumnus_, _alumni_; _alumna_, _alumnae_; _fungus_,
_fungi_; _focus_, _foci_; _radius_, _radii_; _datum_, _data_; _medium_,
_media_; _phenomenon_, _phenomena_; _stratum_, _strata_; _analysis_,
_analyses_; _antithesis_, _antitheses_; _basis_, _bases_; _crisis_,
_crises_; _oasis_, _oases_; _hypothesis_, _hypotheses_; _parenthesis_,
_parentheses_; _thesis_, _theses_; _beau_, _beaux_; _tableau_,
_tableaux_; _Mr._, _Messrs._ (_Messieurs_); _Mrs._, _Mmes._
(_Mesdames_).

Exercise:

Write the singular and plural of the following words: _day_,
_sky_, _lady_, _wife_, _leaf_, _loaf_, _negro_, _potato_,
_tomato_, _pass_, _glass_, _boat_, _beet_, _flash_, _crash_,
_bead_, _box_, _passenger_, _messenger_, _son-in-law_, _Smith_,
_Jones_, _jack-o'-lantern_, _hanger-on_, _stratum_, _datum_,
_phenomenon_, _crisis_, _basis_, _thesis_, _analysis_.

=Compounds=

=78a. Use a hyphen between two or more words which serve as a single
adjective before a noun:= _iron-bound bucket_, _well-kept lawn_,
_twelve-inch main_, _normal-school teacher_, _up-to-date methods_,
_twentieth-century ideas_, _devil-may-care expression_, _a
twenty-dollar-a-week clerk_.

=But when the words follow the noun, the hyphen is omitted.= _The lawn is
well kept. Methods up to date in every way_.

=Also adverbs ending in _-ly_ are not ordinarily made into compound
modifiers:= _nicely kept lawn_, _securely guarded treasure_.

=b. Use a hyphen between members of a compound noun when the second
member is a preposition, or when the writing of two nouns solid or
separately might confuse the meaning:= _runner-up_, _kick-off_;
_letting-down of effort_, _son-in-law_, _jack-o'-lantern_, _Pedro was a
bull-fighter_, _a woman-hater_, _Did you ever see a shoe-polish like
this?_

=c. Use a hyphen in compound numbers from twenty-one to ninety-nine, and
in fractions according to the following examples:=

_Twenty-three_, _eighty-nine_; but _one hundred and one_.
_Twenty-third_, _one-hundred-and-first man_. _Three-fourths_, _four and
two-thirds_, _thirty-hundredths_, _thirty-one hundredths_.

But omit the hyphen in simple fractions when loosely used: _Three
quarters of my life are spent._ _One third of his fortune._

=d. A hyphen is not used in the following common words:= _airship_,
_altogether_, _anybody_, _baseball_, _basketball_, _everybody_,
_football_, _goodby_, _herself_, _handbook_, _himself_, _inasmuch_,
_itself_, _midnight_,