More than a quarter-pint, that's obvious (5)
I believe the answer is:
overt
'obvious' is the definition.
(similar in meaning)
'more than a quarter-pint' is the wordplay.
'more than' becomes 'over' (eg over t00 is more than t00).
'a quarter-pint' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'over'+'t'='OVERT'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for overt that I've seen before include "Obvious, patent" , "This is not hard to see" , "Plain and obvious" , "Open and unconcealed" , "Open, not 1 across" .)