Seed a mythical door-opener! (6)

I believe the answer is:

sesame

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'seed' is the definition.
(sesame seed is a kind of seed)

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

(Other definitions for sesame that I've seen before include "Plant cultivated for its seeds - opening word?" , "Seeds used for making oil" , "Plant with edible seeds" , "Open . . . . . . is a magic phrase to gain entry" , "Crop valued for its seeds and oil" .)

I've seen this clue in the Sydney Morning Herald.

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