Support nobleman in speech (4)
I believe the answer is:
pier
'support' is the definition.
(pier is a kind of support)
'nobleman in speech' is the wordplay.
'nobleman' becomes 'peer' (peer is a kind of nobleman).
'in speech' shows a homophone (sound like).
'peer' is a homophone of 'PIER'.
(Other definitions for pier that I've seen before include "Support member" , "Break-water or landing stage" , "Supporting structure" , "Support for two adjacent bridge spans" , "Quay" .)