slang contraction of is not, are not, am not, do not or does not.

A polite term for shoving a lubricated probe into the Earth's hole to release gas.

informal language;teachers hate it;used in texting,talking

<negative third person singular> Chiefly American Colloquial Contraction

A single word that is equivalent to other words such as:
1) Am not
2) Are not
3) Is not

==> Most likely originated in the Southern States of America as it flows easily with their accent but has now been used in many places around the world.

Is now in a dictionary

Short for "am not" and for nothing else – not even "is not", for "it ain't" would just be "it am not". The only correct use is "I ain't" which is a contraction of "I am not". So, don't say e.g. "you ain't" which would only mean "you am not".