1. A side road where one can turn off
2. (Informal) Something causing antagonism or loss of interest; SYN. negative stimulation.
3. Something that offends you and causes you to lose interest in something or someone is a turnoff. Something about a person of the opposite sex that causes you to lose sexual or romantic interest in that person is a turnoff. A turn-on is the opposite of a turnoff.
4. A road or path that leaves another road or path and travels in a different direction is a turnoff.