Way a sun exists in a constant state (6)
I believe the answer is:
stasis
'a constant state' is the definition.
(static or unchanging state)
'way a sun exists' is the wordplay.
'way' becomes 'st' (abbreviation for street).
'sun' becomes 's'.
'exists' becomes 'is' ('be' can be a synonym of 'exist').
'st'+'a'+'s'+'is'='STASIS'
'in' is the link.
(Other definitions for stasis that I've seen before include "lack of progress" , "lack of activity" , "State of inactivity where nothing moves" , "Period of equilibrium" , "Abnormal state in which the flow of blood is stopped" .)