Definition of "goop"

The flesh [of the mistletoe berry] is sticky, and forms strings and ribbons between my thumb and forefinger. For the mistletoe, this viscous goop – and by the way, viscous comes to English from viscum – is crucial. The stickiness means that, after eating the berries, birds often regurgitate the seeds and then wipe their bills on twigs – leading to the seeds' getting glued to the tree, where they can germinate and begin the cycle anew.

2014 December 23, Olivia Judson, “The hemiparasite season ”, in The New York Times‎, archived from the original on 23 December 2014

I pointed out that Stiffy, who is pure padded cell from the foundation up, was planning to marry the Rev. H.P. Pinker, himself as pronounced a goop as ever preached the Hivites and Hittites

1963, P.G. Wodehouse, Stiff Upper Lip, Jeeves, chapter 22

Airstream, 1977. He showed her ones on eBay that looked like blunt rifle slugs, went for crazy money in any condition at all. The uncle had gooped this one over with white expansion foam, gone gray and dirty now, to stop it leaking and for insulation.

2014, William Gibson, The Peripheral, G. P. Putnam's Sons

Young John blushed at being found “gooping” at himself in the glass.

1925, Margaret Turnbull, Alabaster Lamps‎

He always said vegetables are grown to be eaten, not gooped at. Even a donkey doesn't want a carrot a foot long. I've always remembered. Of course he never won a thing at the Show.

1955, Ring Up the Curtain: Four Plays‎

it was dreadful, it was frightening, to be the sort of woman that, for some unknown reason, all men looked at, all men gooped at, all men—wanted.

1968, Christianna Brand, What Dread Hand: A Collection of Short Stories‎, The Hornet's Nest