Note assailant finally boards craft (8)
I believe the answer is:
crotchet
'note' is the definition.
(musical note)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for crotchet that I've seen before include "A note in music equal to half a minim" , "Quarter of a semibreve" , "One in bar" , "Fancy" , "as mark scored" .)