(archaic or dialectal, chiefly Scotland) To block, obstruct; act detrimentally toward.
[…] , and pressing to have bereft them of their lives by umbesetting of the high gates to that effect at divers times of before, […]
[…] that king on one occasion, April 1535, having to grant a letter of protection in favour of him ‘and his wife and bairns’ against Sir Patrick Hepburn of Wauchtonne and thirty-four others for ‘umbesetting the highway for his slaughter.’
(archaic or dialectal, chiefly Scotland) To overwhelm; cover completely.