E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To lower; to cast down. Brutus complained that he had not lately seen in Cassius that courtesy and show of love which he used to notice; to which Cassius replies, If I have vailed [lowered] my looks, I turn the trouble of my countenance merely on myself. Vexed I am of late [and this may] give some soil to my behaviour.