Slacken rhymes with:
blacken, glacken, bakken, blacken, bracken, chacon, glacken, hakon, machen, macken, mccracken, mccrackin, mcmackin, mcmakin
Slacken sounds like:
salesman, salesmen, saleswoman, saleswomen, saligman, salizzoni, salkin, salsman, salzano, salzman, salzmann, schlossman, seclusion, seligman, seligmann, seligson, selkin, silicon, silicone, silken, slauson, slawson, sleasman, slocan, slocum, slogan, slokum, socialism