Gunslinger would have this tense boatyard worker provided with a measure of alcohol (7,6)
I believe the answer is:
trigger finger
'gunslinger would have this' is the definition.
'tense boatyard worker provided with a measure of alcohol' is the wordplay.
'tense' becomes 't' (abbreviation used in many dictionaries).
'boatyard worker' becomes 'rigger'.
'provided with' says to put letters next to each other.
'a measure of alcohol' becomes 'finger'.
't'+'rigger'+'finger'='TRIGGER FINGER'
(Other definitions for trigger finger that I've seen before include "Gun-firing digit" , "Index digit, when holding gun" , "is one itchy?" , "Firing digit" .)