Overwhelming hospital ultimately and gradually get worse (9)
I believe the answer is:
landslide
'overwhelming' is the definition.
(as in a landslide victory)
'hospital ultimately and gradually get worse' is the wordplay.
'ultimately' indicates one should take the final letters.
'gradually get worse' becomes 'slide' (slide can mean to decline or get worse).
The final letter of 'hospital' is 'l'.
'l'+'and'+'slide'='LANDSLIDE'
(Other definitions for landslide that I've seen before include "Overwhelming electoral victory" , "Overwhelming election win" , "Movement at grass-roots level" , "Huge majority at election" , "easy victory" .)