misadd means to add incorrectly. Lexicurio rates it Rare gem — a strength score of 82 out of 100.
Etymology
From mis- + add.
verb
- To add incorrectly.“And where a barrister, in summing up the items proved before him as arbitrator, misadded them, and thereby by mistake omitted 23l. in favour of the plaintiff, the Court, even at the instance of the barrister, would not allow an amendment, the defendant's counsel objecting.”