Old article about one part of hospital (7)
I believe the answer is:
ancient
'old' is the definition.
('ancient' can be similar in meaning to 'old')
'article about one part of hospital' is the wordplay.
'article' becomes 'an' (indefinite article).
'about' becomes 'c' (abbreviation for 'circa'**).
'one' becomes 'i' (Roman numeral).
'part of hospital' becomes 'ent' (I've seen this in other clues).
'an'+'c'+'i'+'ent'='ANCIENT'
(Other definitions for ancient that I've seen before include "Very old, like the poetic mariner" , "Shakespearean standard-bearer" , "Pistol" , "from olden times" , "Dating from long ago" .)