The word "flossiest" is spelled with a double "s" to convey the pronunciation of a prolonged hiss sound. The IPA phonetic transcription for "flossiest" is /ˈflɒsiəst/ with the stress on the second syllable. The "f" is pronounced with the lower lip touching the upper teeth, followed by the prolonged "s" sound. The "o" is pronounced as in "lot," and the "i" is pronounced as "ee." The "a" in "est" is pronounced as "uh" and the final "t" is silent.
The term "flossiest" is derived from the word "floss", which originated from Old French "flosche" meaning "tuft of wool" or "floche" meaning "nap of a cloth". In the late 17th century, "floss" began to be used in English to refer to soft, silk fibers. Over time, "floss" came to be associated with something of high quality, luxury, or extravagance. The addition of the "-iest" suffix to create "flossiest" simply indicates the superlative form of "floss", implying the highest degree of luxury or extravagance.