Collusively

adv. [f. prec. + -LY².] In a collusive manner; by fraudulent agreement, deceptively.

1746.  W. Thompson, R. N. Advoc. (1757), 49. Both must act collusively, like two knavish Lawyers for a mutual Benefit.

1765–9.  Blackstone, Comm., III. 16 (R.). The land might have been aliened collusively without the consent of the superior.

1849.  Macaulay, Hist. Eng., II. 85. There can be no reasonable doubt that the dissenting judge was … acting collusively.