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"The word "interjection" literally means "thrown in between" from the Latin inter ("between") and iacere ("throw"). Interjections are generally uninflected function words and have sometimes been seen as sentence-words, because they can replace or be replaced by a whole sentence (they are holophrastic). Sometimes, however, interjections combine with other words to form sentences, but not with finite verbs. When an exclamation point is not needed, a comma can take the place." /wikipedia/