Unhappy year when kept outside confines of the stable (6)
I believe the answer is:
steady
'stable' is the definition.
(associated in meaning)
'unhappy year when kept outside confines of the' is the wordplay.
'unhappy' becomes 'sad' (similar in meaning).
'year' becomes 'y'.
'when kept outside' is an insertion indicator.
'confines of' suggests removing the centre (the letters at the borders or confines are used).
'the' with its middle taken out is 'te'.
'sad'+'y'='sady'
'sady' going around 'te' is 'STEADY'.
(Other definitions for steady that I've seen before include "Well-balanced" , "Not subject to change or variation" , "Ovisac of some marine creatures" , "Balanced, not shaky" , "Unwavering" .)