Dead wood, to have the

See quotations.

1857.  Let such men but have a sure thing, or, as Californians say, the deadwood, and they will bet their last farthing.—San Francisco Call, Jan. 7.

1858.  ‘I have the dead wood on him’ was used familiarly [in Kansas], meaning: ‘I have him in my power.’—A. D. Richardson, ‘Beyond the Mississippi,’ p. 134 (Hartford, 1867).

1872.  He considered himself to possess the “dead-wood.”—C. King, ‘Mountains of Sierra Nevada,’ p. 211. (N.E.D.)