The word 'well-reasoned' is a modern English compound adjective formed by combining the intensifying adverb 'well' with the past participle of the verb 'reason'. The core element, 'reason', traces back to Latin ratio, meaning 'calculation, account, understanding', derived from the verb reri ('to think, consider'). The suffix '-ed' converts the verbal concept into an adjectival state. Thus, the literal construction 'thoroughly thought through' elegantly captures the modern meaning of an argument or decision that is logical, considered, and sound.

Structure: well (thoroughly) + reason (logic) + ed (adjective suffix) - well: Old English origin, meaning 'in a good manner, thoroughly'. In this compound, it functions as an intensifying adverb. - reason: From Old French raison, Latin ration- (reckoning, understanding). It functions as the core noun/verb root meaning 'logic, thought'. - ed: Old English origin, a suffix used to form adjectives from nouns or verbs, meaning 'having the quality of'.