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1.
Often used in fantasy writing, it is equivalent to mood or atittude.
'You're moody' becomes something similar to 'you have an agressive demeanour'.
We prefer to talk in terms of moods and atittudes, but in writing "demeanour" sounds much more sophisticated.
"Your demeanour is pleasant"

"His depressive demeanour just flushes the fun out of parties"
by A speaker's curtain November 02, 2006