This is the 12196th most frequent Swedish word.
råttmördare
Rat poison.
The word 'råttmördare' here refers to a substance or a trap designed to kill rats, used literally.
Huset blev snabbt av med sitt problem tack vare den nya råttmördaren.
The house quickly got rid of its problem thanks to the new rat killer.
The word 'råttmördare' refers metaphorically to someone accused (wrongly) of harming rats.
Det visade sig att ingen i sagan var den riktiga råttmördaren.
It turned out that no one in the tale was the real rat killer.
Here 'råttmördare' metaphorically describes someone who is adept at solving issues, likened to eliminating pests.