Civic dignitary from Irish county on seagoing vessel (8)
I believe the answer is:
mayoress
'civic dignitary' is the definition.
(I've seen this before)
'irish county on seagoing vessel' is the wordplay.
'irish county' becomes 'mayo' (I've seen this before).
'on' becomes 're' ('on' can be mean 'with reference to').
'seagoing vessel' becomes 'ss' (abbreviation for steamship).
'mayo'+'re'+'ss'='MAYORESS'
'from' acts as a link.
(Other definitions for mayoress that I've seen before include "Civic dignitary" , "Public official" , "Head of town council" , "Local dignitary" , "Female dignitary" .)