Spineless individual's priority: taking top off, with another hidden (7)

I believe the answer is:

octopus

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'spineless individual's priority' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

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

Can you help me to learn more?

(Other definitions for octopus that I've seen before include "Cephalopod mollusc" , "Cop-outs (anag.)" , "Eight-legged creature" , "army swimmer" , "Eight-armed mollusc" .)

I've seen this clue in The Independent.

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