Three of them in company show great approval (6)
I believe the answer is:
cheers
'three of them in company' is the definition.
I can't tell whether this definition defines the answer.
'show great approval' is the wordplay.
I cannot quite understand how this works, but
'show' could be 'er' (US medical drama) and 'er' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for cheers that I've seen before include "Encouragement" , "Bottoms up; thanks" , "Something said before drinking" , "Cries of approval" , "Expression of gratitude" .)