The compound 'write-down' is a phrasal verb nominalization, formed from the core Germanic verb 'write' and the directional adverb 'down'. The verb 'write' originates from a Proto-Germanic root meaning to tear, scratch, or carve, reflecting early methods of inscribing on hard surfaces. The particle 'down' evolved from an Old English term related to hills, acquiring a figurative sense of moving to a lower, more concrete, or recorded state. When combined, the literal action of "writing something down" onto a surface to make a permanent record evolved into a specific accounting metaphor in the 20th century. In this financial sense, it logically signifies the action of recording an asset's reduced value, bringing its book value "down" to a lower, more realistic figure.

Structure: write (to form letters) + down (to a lower position) - write: From Old English 'wrītan', meaning to score, outline, or form letters. In this compound, it functions as the core verb. - down: From Old English 'dūne', a shortened form of 'of dūne', meaning from the hill. In this compound, it functions as an adverbial particle indicating the direction or completion of the action.