Green’s Dictionary of Slang

heterosexual ‘missionary position’ intercourse; the female enital area; also as adj.

[1785		Grose Classical Dict. of the Vulgar Tongue n.p.: spread eagle a soldier tied to the halberts in order to be whipped, his attitude bearing some likeness to that figure, as painted on signs].
1999		‘Master Pimp’ Pimp’s Rap 198: His body was drenched with sweat. He was stroking with the craftsmanship of a professional cocksman. He was laying heavy pipe to a sister who had her legs spread wide eagle.
2005		Jade LB Keisha the Sket (2021) 82: I woz lyin on da bed spread eagle waitin 4 ricardo 2 enter me.
2013		F. Bill Donnybrook [ebook] ‘[S]he’ll be busy on her back trading spread-eagle for a wage the next few nights’.
2015		asstr.org 🌐 He was able to get one shot of her spread eagle as she fell and panties did little to hide her pussy as it spread open when she tried to catch herself.