Lethal Weapon ends with dark material (5,4)
I believe the answer is:
death star
'lethal weapon' is the definition.
I know nothing about this answer so I can't judge whether this works.
'ends with dark material' is the wordplay.
'ends' becomes 'deaths' ('death' can be a synonym of 'end').
'with dark material' becomes 'tar' (I can't justify this - if you can you should believe this answer much more).
'deaths'+'tar'='DEATH STAR'
Can you help me to learn more?
(Another definition for death star that I've seen is " Empire's enormous battle station (Star Wars)".)