This only completes the details of the correct answers of Alun and Rasputin:
“Drop rain/dew on us, O heavens” more or less.
Ed
]]>And mea culpa, I recognised the imperative case bit, but I failed to notice that caeli was subject case.
]]>Rorate, I think, is the imperative of rorare, so Rorate Caeli is a command for the heavens to drop dew or moisten.
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