27 across
In
rage,
black
a
source
of
energy
(4)
In rage, black a source of energy (4)
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The definition is at the beginning of the clue.
How the clue works
Right, so in rage is your definition here — if you're in a rage, you could say you're boiling or seething. For the wordplay, take B, the abbreviation for black, and stick it in front of OIL, a source of energy, and the two bits together give you the answer.