Crashingly means with a loud, sudden and heavy impact or with a disastrous and crushing effect. The antonyms of crashingly refer to the opposite of these qualities. Some of the antonyms include gently, softly, smoothly, lightly, pleasantly, gradually, slowly, steadily, easily, and quietly. Using an antonym of crashingly in a sentence would mean replacing its meaning with the opposite. For example, instead of saying "the piano crashed to the ground", you could say "the piano landed gently on the ground". The appropriate use of antonyms for crashingly will depend on the context in which it is being used.