dayum Share definition Flag an explative, not unlike whoa. It is a more emphasized version of the word "damn" when it is used in the same way. "Dayum! Your sister's HOT!" dayum by Fatass February 13, 2003 Words you can keep railfan mug chonk mug chud mug based mug 67 mug slime mug mogging mug chopped mug thot mug glazing mug huzz mug yams mug larp mug unc mug cracked mug simp mug baddie mug bop mug lolcow mug