The Pisky would seem to be the 'Brownie' of the Lowland Scot, the Duine Sith of the Highlander, and, if we may judge from an interesting note in Scott's The Pirate, the 'Peght' of the Orkneys.
"The Fairy-Faith in Celtic Countries"
W. Y. Evans Wentz
"I am an honest man minding mine own business, and Sith ye are the same, seek not to hinder me," replied the owner of the Moat Farm.
"The Manor House School"
Angela Brazil
Now whither for succour shall I flee, Sith that Fellowship hath forsaken me?
"A Select Collection of Old English Plays, Volume I."
R. Dodsley