Sword power stops three Europeans (4)
I believe the answer is:
epee
'sword' is the definition.
(sword used in fencing)
'power stops three europeans' is the wordplay.
'three europeans' can mean three replacements for 'european'.
'power' becomes 'p'.
'stops' means one lot of letters goes inside another.
'european' becomes 'E' (abbreviation e.g. EU).
'european' becomes 'E' (abbreviation e.g. EU).
'european' becomes 'E' (abbreviation e.g. EU).
'e'+'e'='ee'
'p' going within 'ee' is 'epe'.
'epe'+'e'='EPEE'
(Other definitions for epee that I've seen before include "Duelling blade" , "Fencing weapon" , "Fighting blade" , "Fencing sword similar to a foil" , "sharp-edged implement" .)