Spray something black? (3)

I believe the answer is:

jet

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

'spray' is the definition.
(I've seen this in another clue)

I can't explain the rest of the clue.

(Other definitions for jet that I've seen before include "Rapid stream of liquid or gas" , "Jumbo plane?" , "Hard black mineral used as gem" , "Hard black mineral or plane engine" , "Kind of plane, or a glossy black" .)

I've seen this clue in the Evening Standard.

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