Tea break really excites workers, first of all (4)
I believe the answer is:
brew
'tea' is the definition.
(brew can informally mean a cup of tea)
'break really excites workers first of all' is the wordplay.
'first of all' suggests taking the first letters.
The first letters of 'break really excites workers' is 'BREW'.
(Other definitions for brew that I've seen before include "Infuse" , "Make beer by boiling and fermentation" , "Ferment rather than distil" , "Mixture" , "Plot" .)