Shoot up, perhaps flying around speed of light (6)

I believe the answer is:

inject

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

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

I cannot understand how the rest of the clue works.

(Other definitions for inject that I've seen before include "Introduce; inoculate" , "Force in" , "Use a syringe" , "Insert via needle" , "Use a needle" .)

I've seen this clue in The Times.

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