foulest
foul-est
adjective
The superlative form of 'foul', meaning most unpleasant, offensive, or morally corrupt.
"That was the foulest smell in the whole kitchen."
Thesaurus
Synonyms: foul, tangled, fouled, afoul, out-of-bounds, nasty, dirty, unclean, filthy, soiled, clog, crap up