(To). To criticise, expose in print, show up, reprove. A scholastic term. Rebellious and idle boys are slated, that is, their names are set down on a slate to expose their offence, and some punishment is generally awarded.
The journalists there lead each other a dance. If one man `slates' another for what he has done, It is pistols for two, and then coffin for one.
Punch (The Pugnacious Penmen), 1885.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894