Blast, say, dynamite left by sailor around vacated emplacement (9)
I believe the answer is:
expletive
'blast say' is the definition.
('blast' is a mild expletive)
'dynamite left by sailor around vacated emplacement' is the wordplay.
'dynamite' becomes 'explosive'.
'left by' suggests deleting specific letters (word is left or abandoned by specified letters ).
'sailor' becomes 'os' (ordinary seaman).
'around' is an insertion indicator.
'vacated emplacement' becomes 'et' (I am not sure about this - if you are sure you should believe this answer much more).
'explosive' with 'os' taken away is 'explive'.
'explive' placed around 'et' is 'EXPLETIVE'.
Can you help me to learn more?
(Other definitions for expletive that I've seen before include "Dirty word" , "Swear word" , "Profane exclamation" , "oath" , "Swearword" .)