Check trainers have been sent (8)

I believe the answer is:

restrain

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'check' is the definition.
(restraining is a kind of checking)

'trainers have been sent' is the wordplay.
'trainers' anagrams to 'RESTRAIN'.
But, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for restrain that I've seen before include "Control - check" , "Stop" , "Keep under control" , "bar" , "stay" .)

I've seen this clue in The Mirror.

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