Tenacious, that man is opening a seedy bar (8)
I believe the answer is:
adhesive
'tenacious' is the definition.
(similar in meaning)
'man is opening a seedy bar' is the wordplay.
'man is' becomes 'hes' (I can't justify this - if you can you should give a lot more credence to this answer).
'opening' indicates putting letters inside (some letters open a gap in others).
'seedy bar' becomes 'dive' (as in a dive bar).
'a'+'dive'='adive'
'hes' going into 'adive' is 'ADHESIVE'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for adhesive that I've seen before include "It sticks things together" , "Substance that sticks" , "Hide vase (anag)" , "Binding" , "Glue, gum" .)