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2.
A grammatical contraction of the words "killer" and "sweet" used to emphasize the positive characteristics and connotations of each respective word. Any thing, act or indivual referred to as "Killa Sweet" must be really really cool. There are no true synonyms for "Killa Sweet", because there is no other phrase in the English language that is able to communicate such an intense level of awesomeness. That is why almost every use of "Killa Sweet" ends in an exclamation point. Anything else would not be able to fully get the message across.

This word originated in South-Eastern Pennsylvania circa 2006.

"Those bapesta kicks are killa sweet!"

"That girl from Georgia is killa sweet!"
by Da Bosshog June 21, 2007
 
1.
A contraction of the words killa and sweet, which forms the adjective meaning "incredibly ridiculously awesome and amazing". The phrase "killa sweet" can only be used to express an astronomical amount of coolness and is the most powerful of the typical words to convey the 21st century's definition of cool (i.e. sweet, nice, awesome, gnarly, vicious, killer, tight, bangin'). Killa Sweet is so stupefyingly formidable, that it is almost always used with an exclamation point.

The overwhelming power of the phrase "killa sweet" has limited its useage to some extent. Truth be told, there's not much in this world that merits the use of such a word, and its originators have speculated that the world is "just not ready" for it yet. Included below are a few possible examples where killa sweet can be used:
Man, those new bapestas are killa sweet!

That backboard shattering dunk by Amare Stoudemire was killa sweet!

Winning the lottery is killa sweet!
by Rob da bosshog May 30, 2007