Crossword Genius

Such men may take turns as openers (3)

Ross

I believe the answer is:

key

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

But I can't explain it at all! Could you help me understand?

(Other definitions for key that I've seen before include "Scale system for music" , "Eg, Ctrl, Alt or Esc" , "Device for lock" , "It can open" , "Of crucial importance" .)

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