The compound noun 'swearing-in' is a modern English formation built from the phrasal verb 'to swear in'. Its core, 'swear', descends from the Proto-Germanic \swarjan-, carrying the ancient sense of making a solemn declaration, often invoking a deity as witness. The addition of the particle 'in' completes the verbal action, signifying the formal induction into an office or role through this oath. The '-ing' suffix nominalizes the entire action, transforming the process into the name for the ceremonial event itself. Thus, the term's logic is transparent: it literally denotes "the act of swearing to enter (an office)."

Structure: swear (to take an oath) + ing (present participle) + in (completing an action) - swear: From Old English swerian, meaning to take an oath, promise solemnly. A Germanic root. - ing: A suffix forming the present participle of verbs, from Old English -ende. - in: A preposition/adverb, from Old English in, indicating entry, inclusion, or the completion of an action.