Lariat swallowed the Spanish article — it is actually la reata (the rope), but English speakers heard the article and noun as one word, just like alligator absorbed el lagarto.
A lasso or long rope with a running noose, used for catching livestock; also, a rope used for tethering animals.
From Spanish la reata (the lasso), from reatar (to tie again, to retie), from re- (again) + atar (to tie), from Latin aptāre (to fasten, to fit). The Spanish definite article la was absorbed into the English word, so lariat literally means the retying rope. Key roots: aptāre (Latin: "to fasten, to fit").
Lariat is a perfect example of an article getting swallowed into a loanword. The Spanish is la reata (the rope), but English speakers heard "lariat" as a single word rather than an article-plus-noun combination. The same thing happened with alligator (from Spanish el lagarto, "the lizard") and