Way a sibling creates state of inactivity (6)
I believe the answer is:
stasis
'state of inactivity' is the definition.
(I've seen this before)
'way a sibling' is the wordplay.
'way' becomes 'st'.
'sibling' becomes 'sis' (I have seen 'Little sibling ' mean 'sis' so perhaps 'sibling' could also mean 'sis').
'st'+'a'+'sis'='STASIS'
'creates' acts as a link.
(Other definitions for stasis that I've seen before include "Stoppage of blood flow in body" , "Stoppage of blood circulation" , "Enduring state" , "Secret police force's" , "Assist in state of stagnation" .)