From eccentric, tired, a rant (6)
I believe the answer is:
tirade
'rant' is the definition.
(both can mean an angry outburst)
'from eccentric tired a' is the wordplay.
'tired a' can be anagrammed to 'TIRADE'.
However, I'm not sure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for tirade that I've seen before include "Broadside of denunciation" , "A long abusive denunciation" , "Prolonged speech of abuse" , "A long, abusive outburst" , "A prolonged outburst of abuse" .)