Green’s Dictionary of Slang

1. (US) hair oil.

1932		Dly Jrnl (Vineland, NJ) 27 Apr. 4/4: Salesmen with slickum on hair and moustaches.
1946		Mezzrow & Wolfe Really the Blues 22: Those shirts made us look like a gang of barber poles topped with slickum.
1952		Santa Cruz Sentinel (CA) 4 Dec. 41/7: You can choose slickum for the hair.
1961		Dayton Dly News (OH) 21 Sept. 28/3: The infielder would [...] run his hands through his hair and apply slicum.
1970		Abilene Reporter-News (TX) 11 June 16/3: I use ‘slickum’ for the hair that I still have.
1985		Tampa Trib. (FL) 5 Feb. 53/4: The emcee had [...] starch in his collar and slickum on his hair.

2. in fig. use, superficial, temporary gloss .

1999

Detroit Free Press (MI) 18 June 39/3: A glossy, teched-up ‘To Catch a Thief’ [...] But it’s pleasures are quickly forgotten: it’s all slickum, no stickum.