The word 'to-do' is a straightforward nominalization of the common English infinitive phrase "to do." It emerged in the late 16th century, directly mirroring the structure of the verbal phrase. The logic of its formation is transparent: the action or state implied by "to do" (i.e., things that are to be done) becomes a noun describing either the list of those things or, by figurative extension, the fuss or activity associated with getting them done. This process of converting a verb phrase into a compound noun is a productive feature of English, creating a term that efficiently encapsulates both a plan of action and the commotion it may involve.

Structure: to + do 'to' (Old English preposition/adverb particle) + 'do' (Old English verb).