The UK weather forecast has been predicting blood rain this week, and the BBC site gives an account of what blood rain actually is (see here). It is rain containing particles of sand from deserts. I haven’t seen any evidence of it so far yet this week, although I have noticed that my car, windows etc have had light dustings of reddish dirt or powder in the past, which presumably was the result of the same phenomenon.
The term blood rain is in the OED, with the first citation dating from 1612 (where the spelling is bloud-raine). Its definition is: “rain that is reddish in colour, esp. because of suspended dust or (less commonly) green algae containing red carotenoid pigments”.
The BBC article says that the 12th century historian Geoffrey of Monmouth referred to blood rain. That would have been in Latin, since that was the language he wrote in.