The spelling of the word "betwixt betweens" can be tricky because it is a blend of two words - "betwixt" and "between". The proper spelling is "betwixt and between," but sometimes it's shortened to just "betwixt betweens." The pronunciation is also unique, with the letter "x" making a "ks" sound, so it's pronounced "buh-twihks buh-tweens." The IPA phonetic transcription for this word would be /bəˈtwɪks bɪˈtwinz/. Despite the odd spelling and pronunciation, "betwixt betweens" effectively conveys the idea of being in between two things.
The word "betwixt" is derived from Middle English "bitwix", which comes from Old English "betwyx". In Old English, "betwyx" was a combination of "be-" (meaning "by" or "around") and "twēon" (meaning "two"). Gradually, "betwixt" came to be used as a preposition meaning "between" or "among", specifically referring to a position intermediate or in the middle of two things or places.
On the other hand, "betweens" is the plural form of "between". The suffix "-s" is added to indicate plurality. Nonetheless, "betweens" can also refer to sewing needles that are shorter than the usual length, used for fine or delicate work. In this context, the origin of "betweens" as a noun is unrelated to the etymology of "betwixt".