@igelsQTs It just means to slow or delay in English. In the days after leaded gas was phased out, my dad would have to retard the timing on his muscle car. The octane rating wasn't great during those days and it could cause predetonation. He did build the transmission and motor for performance.

There's boost retard too. It's not commonly called that but when positive pressure is made with a supercharger, the ignition is delayed.

It was also used to describe people who were disabled.