Green’s Dictionary of Slang

1. a liquid or viscous substance or mixture.

1945		N.Y. Times Mag. 4 Nov. 12/3: The somewhat pleasanter words, mostly referring to food, such as ‘glop’, meaning any food mixture.
1953		Berrey & Van den Bark Amer. Thes. Sl. (2nd edn).
1976		N. Thornburg Cutter and Bone (2001) 109: And now in her glop-rimmed eyes the pain was raw, exposed.
1987		P. Muldoon ‘The Soap-Pig’ in Meeting the British in Penguin Bk Contemp. Irish Poetry 386: [...] It’s a bar of soap / [...] / that I work each morning into a lather, / with my father’s wobbling-brush, / then reconcile to its pool of glop / on my mother’s wash-stand’s marble top.
1999		T. Dorsey Florida Roadkill 152: A glop of slaw hit Veale in the ear.

2. food, usu. unappetizing .

1944		P. Kendall Dict. Service Sl. n.p.: glop . . . unappetizing food.
1997		P. Theroux Kowloon Tong 88: The fish heads, the pig’s feet, the spongy tripe, the tendons, fifteen courses of this glop were not unusual.
2012		L. Berney Whiplash River [ebook] The food wasn’t bad. It was the glop made of tomatoes, onions, rice, and chickpeas.

3. (US) silly nonsense.

1952		cited in Wentworth & Flexner DAS.
1960		B. Wohl A Cold Wind in August (1963) 198: You can hardly expect him to be talking a lot of glop into the phone.
1972		Dahlskog Dict. Contemp. and Colloq. Usage.

4. (US) used of an individual, sluggish, lacking spirit.

1966

Catholic Transcript 2 Sept. 19/2: Miss Trahey wasn’t happy with how she herself came across. ‘The girl who plays me on the screen (June Harding) is too nebbishy. She’s a glop’.