Explain meaning of hollow decree and penalty issued (6)

I believe the answer is:

define

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'explain' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for define that I've seen before include "Describe exactly" , "Characterise" , "State the meaning of" , "Explain the meaning of a word" , "Fix the meaning of" .)

I've seen this clue in The Irish Times.

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