Promising remedy's first found in arm of the sea (6)

I believe the answer is:

bright

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

'promising' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for bright that I've seen before include "Clever; fine" , "Intelligent; vivid" , "Vivid; cheerfully lively" , "Radiant or intelligent" , "Dazzling or intelligent" .)

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

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