lone hand

Cards.

a person who holds a hand so strong that he or she can play a deal without the hand of his or her partner.
the hand played by such a person.

a person who by preference conducts his or her affairs without the advice or assistance of others: a lone hand in investment circles.

a stand or action taken independently: a lone hand in the trade negotiations.

Origin of lone hand

First recorded in 1790–1800

Whatever the cause, it was plainly enough to be seen that the heavy knot had not cracked the Lone-Hand Kid's spine.

From Place to Place |Irvin S. Cobb
The influence of this lone-hand way of playing the game extends very far.

The Life and Letters of Walter H. Page, Volume II |Burton J. Hendrick
Whatever his innermost emotions may have been, his expression gave no hint that the mouthings of the Lone-Hand Kid had sunk in.

From Place to Place |Irvin S. Cobb
He actually quitted his cell (for the only occasion on record) and started on a lone-hand raid against his adversaries stronghold.

The Cradle of Mankind |W.A. Wigram

It is because of all these things that Barry had preferred to make this particular photographing trip a lone-hand one.

Air Men o' War |Boyd Cable

lone hand

(in card games such as euchre) an independent player or hand played without a partner

play a lone hand to operate without assistance