Complaint from mothers about parking (5)
I believe the answer is:
mumps
'complaint' is the definition.
(mumps is a kind of disease)
'mothers about parking' is the wordplay.
'mothers' becomes 'mums' (mum is a kind of mother).
'about' indicates putting letters inside.
'parking' becomes 'p' (abbreviation on road signs).
'mums' going around 'p' is 'MUMPS'.
'from' is the link.
(Other definitions for mumps that I've seen before include "Infectious glandular disease" , "Viral disease with swellings" , "Virus disease causing painful swellings in neck" , "Swollen-face disease" , "harmful disease" .)