Siegfried finally entering Ring cycle (5)
I believe the answer is:
pedal
'cycle' is the definition.
(pedal can mean to cycle a bicycle)
'siegfried finally entering ring' is the wordplay.
'finally' says to take the final letters.
'entering' is an insertion indicator.
'ring' becomes 'peal' (pealing is a kind of ringing).
The final letter of 'siegfried' is 'd'.
'd' put into 'peal' is 'PEDAL'.
(Other definitions for pedal that I've seen before include "Bicycle footrest" , "cause a revolution in cycling?" , "sustained note" , "Of or relating to the feet" , "Part of cycle" .)