Crossword Genius

So, fierce type's in retreat (4)

Ross

I believe the answer is:

ergo

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

'so' is the definition.
(synonyms)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for ergo that I've seen before include "for this reason" , "Hence" , "'Cogito, ---- sum'" , "Therefore - what a goer" , "as a consequence" .)

I've seen this clue in The Everyman puzzle in The Observer.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.