Green’s Dictionary of Slang

slick v.

[SE slick]

1. [mid-19C] (also slick over) to get something finished with or disposed of quickly.

2. [mid-19C+] to swindle, to hoax, to cheat.

In phrases

slick-’em-plenty (n.) [racial stereotyping both as to ethics and occupation] [1970s] (US black)

a derog. term for a Jew, implying duplicitous, persuasive talk .

slick (oneself) up (v.)

1. [mid-19C+] (US) to tidy (oneself), to make neat; thus slicked up, tidy.

2. [1910s–50s] in fig. use, to arrange, to defeat, to ‘make good’.

slick over (v.)

see sense 1 above.