Neptune’s satellite’s interval discharging energy (6)

I believe the answer is:

triton

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'neptune's' is the definition.
(I've seen this in another clue)

I don't understand how the rest of the clue works.

(Other definitions for triton that I've seen before include "Horn-blower" , "Moon" , "Son of Poseidon, shown as man with fish's tail with trident and shell-trumpet" , "conch-blowing deity" , "Minor Greek god" .)

I've seen this clue in The Times.

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