Space close to patient with bad disorder (7)
I believe the answer is:
entropy
'disorder' is the definition.
(thesaurus)
'space close to patient with bad' is the wordplay.
'space' becomes 'en' (in printing, a space as wide as a letter 'n').
'close to' indicates one should take the final letters (the close/ending of).
'with' means one lot of letters go next to another.
'bad' becomes 'ropy' (ropy can mean bad quality).
The last letter of 'patient' is 't'.
'en'+'t'+'ropy'='ENTROPY'
(Other definitions for entropy that I've seen before include "Degree of disorder (physics)" , "state of increasing disorder" , "Tory pen (anag) - measure of disorder" , "Measure of the disorder of a system" , "Term in physics" .)