a device (such as a fan) that introduces fresh air or expels foul air

a device (such as a fan) that introduces fresh air or expels foul air

At that time; then, conjunction_ Used after a comparative adjective or adverb to introduce the second element or clause of an unequal comparison, When. Used especially after hardly and scarcely, A particle expressing comparison, used after certain adjectives and adverbs which express comparison or diversity, as more, better, other, otherwise, and the like. It is usually followed by the object compared in the nominative case. Sometimes, however, the object compared is placed in the objective case, and than is then considered by some grammarians as a preposition. Sometimes the object is expressed in a sentence, usually introduced by that, preposition_ introduces a comparison, and is associated with comparatives, and with words such as more, less, and fewer. Typically, it seeks to measure the force of an adjective or similar description between two predicates, In comparison or contrast with

the act of beginning something new, the act of putting one thing into another, That part of a book or discourse which introduces or leads the way to the main subject, or part; preliminary; matter; preface; proem; exordium