Dinosaur disregarding rodent and duck shows muscle (7)

I believe the answer is:

triceps

I'm a little stuck... Click here to teach me more about this clue!

'muscle' is the definition.
(I know that triceps is a muscle)

I don't understand the remainder of the clue.

(Other definitions for triceps that I've seen before include "Muscles" , "Green citrus fruit" , "Source of uplifting strength" , "One stretches out an arm!" , "Muscle at the back of the upper arm" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app