Yes, it is an adverb, the adverb form of the adjective respectful.
The noun or verb respect has the derivative adjective respectful and the adverb form respectfully.(The related adverb respectively means with respect to order or form.)
No, the word "respectable" is not an adverb.The word "respectable" is an adjective.The adverb form of the word "respectable" is respectably.
The noun civility is related to the adjective 'civil" (the social meaning). The adverb for is civilly (politely, respectfully).
more respectfully for comparative and most respectfully for superlative
No.
with due respectfully
Respectfully sheweth is used for Respectfully submitted
As an adjective or an ending to a letter. For example, "He respectfully held the door open." or "Respectfully, [Your name here]"
very Respectfully
He helped the old man respectfully?
The "R" of respectfully is capitalized at the end of minutes.
Say that you respectfully decline?