Crossword Genius

Fearful, with missing millions fast accumulating? (8)

Ross

I believe the answer is:

trebling

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 trebling that I've seen before include "Increasing threefold" , "Multiplying by three" .)

I've seen this clue in The Times.
Want a hint initially instead of a full solution? Install my app