Had got together, one understood (8)
I believe the answer is:
gathered
'understood' is the definition.
('gather' can be a synonym of 'understand')
'had got together one' is the wordplay.
I cannot really see how this works, but
'had' could be 'd' (in contractions e.g. 'I'd', 'you'd' etc) and 'd' is found within the answer.
'one' could be 'the' (both can introduce a definite example of something) and 'the' is located in the answer.
The remaining letters 'gare' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gathered that I've seen before include "Understood" , "Collected - inferred" , "Concluded from evidence" , "Accumulated, brought together" , "Collected or assembled together" .)