The word 'unsweetened' is a modern English compound formed through a clear, logical process of affixation. Its core is the Old English adjective 'sweet,' which traces back to the Proto-Germanic swōtuz and ultimately to the Proto-Indo-European root swād- (pleasant, sweet). The verb 'sweeten' was created by adding the causative suffix '-en' (to make) to this root. The past participle 'sweetened' thus means "made sweet." Finally, the Old English negative prefix 'un-' is applied to create the adjective 'unsweetened,' literally meaning "not made sweet." This transparent construction directly reflects its precise modern meaning, describing a food or drink from which added sweetness has been deliberately omitted.

Structure: un (not) + sweet (sweet) + ened (made, having the quality of) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - sweet: The root word from Old English swēte, of Germanic origin, meaning "having the pleasant taste characteristic of sugar." It functions as the core adjective. - ened: A suffix derived from the past participle ending -ed of the verb sweeten, which itself is formed with the verb-forming suffix -en (to make). Here, it functions to indicate the state of having been processed or made to be a certain way.