adverb/sal.mɑ̃/
dirty, dirtily; Intensitive adverb : very, really. (in a bad way) "J'ai été salement amoché par une crise néphrétique" (André Gide, Letters) : "I've been really banged-up by renal crisis"; Related to the precedent (antiphrasis) : very, really (in a good way) " Faut acheter des sardines … C'est salement bon !" (Louis Pergaud, La Guerre des boutons) : "We got to buy sardines … It's really good !"
From sale + -ment.