Blow that is with queen's sword (6)
I believe the answer is:
rapier
'sword' is the definition.
(sword used in fencing)
'blow that is with queen's' is the wordplay.
'blow' becomes 'rap' (rap is a kind of blow).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'with' is a charade indicator (letters next to each other).
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'rap'+'ie'+'r'='RAPIER'
(Other definitions for rapier that I've seen before include "Straight narrow sword with two edges" , "fencing equipment" , "A small spring flower" , "Thin sharp sword" , "A thin double-edged sword" .)