chef-lieu, chefs-lieux, _chief town_, _chief towns_. chou-fleur,
choux-fleurs, _cauliflower_.
2. When two nouns are connected by a preposition, the first only takes
the plural ending, as:
arc-en-ciel, arcs-en-ciel, _rainbow_, _rainbows_. chef-d'oeuvre,
chefs-d'oeuvre, _masterpiece_, _masterpieces_.
N. B.--Peculiar are tête-à-tête, _private interview_, and pied-à-terre,
_temporary stopping-place_, which are invariable.
3. A noun and adjective forming a compound take both the plural ending,
as:
basse-cour, basses-cours, _poultry-yard_, _poultry-yards_.
porte-cochère, portes-cochères, _carriage entrance_, _carriage
entrances_.
N. B.--Peculiar are:
grand'mère, grand'mères, _grandmother_, _grandmothers_.
grand'messe, grand'messes, _high mass_, _high masses_.
monsieur, messieurs, _mister_, _sir_, _gentlemen_.
madame, mesdames, _madam_, _ladies_.
mademoiselle, mesdemoiselles, _miss_, _young ladies_.
4. When a compound is formed of a noun joined to either a verb, a
preposition, or an adverb, then the noun alone takes the sign of the
plural--provided, however, it conveys the idea of plurality, as:
passe-port, passe-ports, _passport_, _passports_.
avant-garde, avant-gardes, _vanguard_, _vanguards_.
contre-maître, contre-maîtres, _foreman_, _foremen_.
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5. Of the following compounds the nouns take _s_ in both numbers,
because they suggest plurality, as:
un, _a_, essuie-mains, _towel, towels = that which dries the hands_.
_or_ cure-dents, _toothpick, toothpicks = that which picks the teeth_.
des, _some_ porte-clefs, _turnkey, turnkeys = one who carries keys._