One of the Holy Grail sexual acts. This involves one man and three women. The lucky man will have one woman on his penis and one hand in each of the other two women. This makes him look like Neptune's tri-pronged trident.

And like everything nautical, the whole thing smells of fish and is very slippery.
Nick: "I scored big the other day, I hit on three chicks and they did Neptune's trident with me."
Dude: "Way to go my man! You IS a sex god!"
by Wizards Sleeve May 7, 2007
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When a woman is laying naked on her stomach, you put your thumb in her ass, 2 fingers in her vagina, and your pinky massages her clitorus.
I went over to my woman's house, and gave her the ole Neptune's Trident until she blacked out.
by Blade_Slasher June 30, 2021
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