Downright and Dead on

Downright adjective - Being or characterized by direct, brief, and potentially rude speech or manner.

Dead on and downright are semantically related In some cases you can use "Dead on" instead an adjective "Downright".

Downright and dead on are semantically related in particular topic. Sometimes you can use "Downright" instead an adjective phrase "Dead on", if it concerns topics such as accurate.