A slip of the pen; a mistake made while writing (e.g., writing a wrong name or address).
名前を間違えて書き損じてしまったので、新しいはがきを買った。
I made a mistake writing the name, so I bought a new postcard.
書き損じを防ぐために、下書きをしてから清書する。
To avoid slips of the pen, I draft first and then write the final copy.
An item ruined by a writing mistake (e.g., a postcard with an incorrect address). Such items are sometimes exchangeable or can be redeemed.
郵便局で書き損じ葉書を他の切手やはがきに交換してもらった。
I had the post office exchange my miswritten postcard for other stamps or postcards.