Non-PRO English Other General / Conversation / Greetings / Letters crossword puzzle

I'm doing a crossword puzzle and I've reached that stage where nothing seems to work, my brain included. I even stooped as low as to look at the easy clues :)

I have letters "s_o_t".
Cryptic clue: "Move quickly to Cos for a break".
Easy clue: "shift fast".

It must be ridiculously easy, but I've been looking at it for 20 minutes now with no result. Help :))