Complexity of small section attached to hospital (5)
I believe the answer is:
depth
'complexity' is the definition.
(thesaurus)
'small section attached to hospital' is the wordplay.
'small section' becomes 'dept' (short for department; 'small' asks for a short form).
'attached to' is a charade indicator (letters next to each other).
'hospital' becomes 'h' (abbreviation for hospital on maps).
'dept'+'h'='DEPTH'
'of' is the link.
(Other definitions for depth that I've seen before include "Downward extent" , "Measurement from front to back" , "Intensity (of emotion)" , "Measure" , "Thoroughness" .)