Acknowledge hospital is having trouble (4)
I believe the answer is:
Here is my best explanation:
'acknowledge' is the definition.
'hospital is having trouble' is the subsidiary indication.
'hospital' becomes 'h'.
'is having' means one lot of letters go next to another.
'trouble' becomes 'ail' ('ail' can be a synonym of 'trouble'**).
(Other definitions for hail that I've seen before include "Frozen rain or Roman greeting", "come down hard", "fall", "Stones falling", "Call, a taxi say", "Falling ice pellets", "word", "Ice pellets - greeting", "Word of greeting" and "volley".)