noun
slip of the pen; mistake in writing
Refers to the act or result of making a writing error, such as a misspelling or wrong character.
See also: 書き損じ
手紙に書き損ないがあったので、書き直した。
There was a slip of the pen in the letter, so I rewrote it.
noun
something ruined by a writing mistake
Often refers to a physical item like a postcard or form that is spoiled because of a writing error.
See also: 書き損じ
書き損ないの葉書が何枚か出た。
I ended up with several postcards ruined by writing mistakes.
Synonym; 書き損じ is more common and can also refer to the act of making a mistake in writing, while 書き損ない often emphasizes the ruined result.
Compound of 書き (kaki, continuative form of 書く 'to write') + 損ない (sokonai, continuative form of 損なう 'to fail, to spoil').