The Portuguese were the first Europeans to make contact with the Kingdom of Siam more than 500 years ago in 1511. In 1518 was signed the Treaty of Friendship and Commerce between Siam and Portugal. Not surprisingly the Thai language absorbed a few terms from the Portuguese.
กะละแม (kalamae): a kind of Thai toffee, from caramelo
คริสตัง (khritsatang): Roman Catholic, from cristão
ปัง (pang, commonly ขนมปัง or khanompang): bread, from pão
สบู่ (sabu): soap, from sabão
สันตะปาปา (santapapa): pope, from santo papa
เหรียญ (rian): coin, medal, from real
Do let me know @PortugueseAsia if you know of other words to be added to the list.