In a way, a half of bitter is always diluted (6)
I believe the answer is:
watery
'always diluted' is the definition.
'watery' can be an answer for 'diluted' (similar in meaning). I'm not certain of the 'always' bit.
'in a way a half of bitter' is the wordplay.
'in' indicates putting letters inside.
'a half of' means to take half the letters.
'bitter' halved is 'ter'.
'way' going around 'ter' is 'WATERY'.
'is' is the link.
Can you help me to learn more?
(Other definitions for watery that I've seen before include "(Of food) thin, tasteless" , "Overly diluted, thin" , "Insipid" , "Weak, too diluted" , "Dilute; weak, pale" .)