Interjection

Interjections (Hey!).
Show excitement (Yow!).
Or emotion (Ouch!).

They're generally set apart from a sentence by an exclamation point, or by a comma when the feeling's not as strong

_{(Darn, that's the end.)}

--Schoolhouse Rock

In`ter*jec"tion (?), n. [L. interjectio: cf. F. interjection. See Interject.]

1.

The act of interjecting or throwing between; also, that which is interjected.

The interjection of laughing. Bacon.

2. Gram.

A word or form of speech thrown in to express emotion or feeling, as O! Alas! Ha ha! Begone! etc. Compare Exclamation.

An interjection implies a meaning which it would require a whole grammatical sentence to expound, and it may be regarded as the rudiment of such a sentence. But it is a confusion of thought to rank it among the parts of speech. Earle.

How now! interjections? Why, then, some be of laughing, as, ah, ha, he! Shak.

© Webster 1913.