RULE XVI.

Compound nouns whose parts are connected by a hyphen accept of the sign

of the plural after that part which essentially constitutes the noun; as,

knight-errant, _knights-errant_; son-in-law, _sons-in-law_; man-of-war,

_men-of-war_; step-child, _step-children_; ember-day, _ember-days_;

man-singer, _men-singers_.