Predator concealing most of his weapon (8)

'weapon' is the definition.
(falchion is a kind of weapon)

'predator concealing most of his' is the wordplay.
'predator' becomes 'falcon' (falcon is a kind of predator).
'concealing' means one lot of letters goes inside another.
'most of' means to remove the last letter.
'his' with its final letter removed is 'hi'.
'falcon' going around 'hi' is 'FALCHION'.