Creep visiting hospital catches cold (4)
I believe the answer is:
inch
'creep' is the definition.
(I've seen this in another clue)
'visiting hospital catches cold' is the wordplay.
'visiting' becomes 'in' ().
'hospital' becomes 'H' (abbreviation for hospital).
'catches' indicates putting letters inside.
'cold' becomes 'C' (eg on taps).
'in'+'h'='inh'
'inh' enclosing 'c' is 'INCH'.
(Other definitions for inch that I've seen before include "0.08333 of a foot" , "Edge along" , "Move slowly and cautiously" , "Imperial unit of length" , "Move in tiny increments" .)