The word "unseven" may seem peculiar because "seven" is not a verb that can be "un-"ed. However, in this case, "unseven" means to undo or reverse the action of counting to seven. The IPA phonetic transcription of this word is /ʌnˈsɛvən/, the stress falling on the first syllable. The first two letters "un-" signify negation or reversal, followed by the familiar word "seven." Even if it sounds strange, "unseven" can still be correctly spelled and understood.
The word "Unseven" is a neologism and does not have an established etymology. As a non-existing word, it doesn't have a historical origin or a linguistic history. It appears to be a combination of the prefix "un-" (meaning "not" or "opposite of") and the number "seven". The exact intention or meaning behind "Unseven" would depend on the context in which it is used.