Look at those irregular adverbs:
C'est un refus absolu: je refuse absolument.
It's an absolute refusal: I refuse absolutely.
C'est un joli décor: vous avez joliment transformé cette scène.
It's a pretty set: you prettily transformed this stage.
C'est vrai: on l'a vraiment fait.
It's true: we really did it.
Although regular adverbs are formed from feminine adjectives by adding -ment (see Forming regular adverbs with -ment), when the masculine form of the adjective ends in any other vowel than a silent e, the adverb is formed from the masculine form instead of the feminine.
