Stately creature, top of stairs, looking sickly (4)
I believe the answer is:
swan
'stately creature' is the definition.
'top of stairs looking sickly' is the wordplay.
'top of' says to take the initial letters.
'looking sickly' becomes 'wan'.
The first letter of 'stairs' is 's'.
's'+'wan'='SWAN'
(Other definitions for swan that I've seen before include "Large water bird" , "... Australian river" , "Stately aquatic bird" , "Cob - pen" , "Mute, whooper or Bewick's bird" .)