Aural means of or relating to the sense of hearing.
That could be interlocution, dialog, chat, discussion, or talk.
'Mean' in this context means 'average'. Thus, 'mean word length' means 'average word length'. This is the total number of letters in your piece of writing, divided by the total number of words.Here...
Border, boundary, edge, limit.
Scary, Creepy, Mysterious, haunted, horrendous, electrifying.