Intern left out of feature on Navy (6)

I believe the answer is:

detain

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'intern' is the definition.
(I know that intern is a more specific form of the action detain)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for detain that I've seen before include "Hold or keep back, maybe for questioning" , "Keep waiting or under restraint" , "Hold (someone) back" , "Stop" , "Hold in detention" .)

I've seen this clue in The Independent.

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