Green’s Dictionary of Slang

easy n.

(US) a gullible person [easy mark under mark n.1 ].

[US]O. Kildare Good of the Wicked 12: If people in our neighborhood had more money to spend, and if there was as many easies as up town, there would be the same electric lights and other fixings that can hide a whole lot on the outside.

SE in slang uses

In phrases

on the easy (adv.)

(US) without effort; easily.

[US]J. Ridley Everybody Smokes in Hell 70: She was the kind of chick who could’ve had a lot of what she wanted on the easy, but what she wanted was to work for what she got.