Crossword Genius

So enthused (half of the time) (4)

Ross

I believe the answer is:

thus

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

'so' is the definition.
(I know that so can be written as thus)

'enthused half of the time' is the wordplay.
'THUS' is hidden in amongst the letters.
However, I'm uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for thus that I've seen before include "As a result" , "'So, therefore (4)'" , "In this manner" , "It follows" , "Consequently" .)

I've seen this clue in The Sunday Times and The Times.
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