Base, initially seeming old, rather, was suitable (6)
I believe the answer is:
sordid
'base' is the definition.
(thesaurus)
'initially seeming old rather was suitable' is the wordplay.
'initially' says to take the initial letters.
'was suitable' becomes 'did' (to 'do' can be to be suitable for a task or job).
The first letters of 'seeming old rather' is 'sor'.
'sor'+'did'='SORDID'
(Other definitions for sordid that I've seen before include "'Dirty, morally degrading (6)'" , "Seedy, squalid" , "Squalid and depraved" , "Dirty, depressing and squalid" , "Dirty and unpleasant" .)