Observed to be like a warmish drink (7)
I believe the answer is:
noticed
'observed' is the definition.
('notice' can be a synonym of 'observe')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for noticed that I've seen before include "remarked" , "Realised" , "Detected" , "regarded" , "Became aware of" .)