Loudly or noisily. Also aloud will work
loudly...
Lound
The antonym of the word 'synonym' is 'antonym'.
The word silently, like most (but not all) words that end in -ly, is an adverb.
silently
An antonym for silent is loud, the antonym for silently is loudly, or aloud.
Silenced
aloud
Noisily
loudly...
The opposite of noisily is quietly or silently.
Lound
There do not seem to be any antonyms with a long O sound. There are the words loudly and noisily, which have the OW and OI sounds, respectively.
Silently is the correct spelling.
Silently is an adverb. Many adverbs end in the prefix -LY.
The word silently *is* an adverb. The adjective form is "silent."
"Silently" is an adverb and it almost always modifies a verb. "He tiptoed silently into the room." "She didn't speak, but her eyes silently followed him as he entered."