IPA: /ˈoʊvərˌvoʊt/
KK: /ˈoʊvərˌvoʊt/
A ballot that indicates more choices or candidates than permitted in a specific election or vote.
The election officials had to disqualify several ballots due to an overvote.
Overvote is formed from "over-" (meaning excessively or beyond) and "vote" (from Latin "votum", meaning a wish or a vow). The word refers to casting more votes than allowed, thus exceeding the permissible limit.
Think of going 'beyond' ('over-') the allowed number of 'votes' — that's why 'overvote' means to cast too many votes.
No commonly confused words.