Maybe you heard -гүй (-gui) as -kui. It's a suffix that adds a negative meaning to the previous word. For example: мөнгөгүй (money-less) and чадахгүй (can-not) and ирэхгүй (will not come/arrive). Or it might also be -хуй/-хүй as af5gw4 suggested (whether it's хуй or -хүй depends on the vowel harmony). It's a suffix that makes a verb into a noun. But it is kind of outdated suffix or it's more commonly used in formal context. You won't hear it much in modern basic daily conversations. As an example, yншихуй (read-ing).

-хуй makes the verb noun. jee/chee ending = -ed