Extremely huge stick can be a ruler (5)
I believe the answer is:
herod
'a ruler' is the definition.
(I have seen 'Infanticidal king' mean 'herod' so perhaps 'king' could also mean 'herod')
'extremely huge stick' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'stick' becomes 'rod' (I've seen this before).
'huge' with its centre removed is 'he'.
'he'+'rod'='HEROD'
'can be' is the link.
(Other definitions for herod that I've seen before include "Former king" , "NT king" , "Infanticidal king" , "Cruel king" , "King of Judea in the time of Jesus" .)