The Vietnamese cognate of kuai tiao named in the Pad Thai article is Hủ tiếu.
Kuai tiao is a Thai borrowing from the Teochew Chinese term guê diao, referring to a type of Chinese rice noodle. The word spread across Southeast Asia through Chinese migration and became adapted to local languages and cuisines.
The Vietnamese form, hủ tiếu, usually refers to a noodle dish or its noodles, especially in southern Vietnam. Related forms include kuyteav in Cambodia and kway teow in Malaysia and Singapore. These are linguistic relatives, not necessarily identical dishes.
A common mix-up is treating hủ tiếu as another name for phở. Phở uses a different culinary tradition and is typically associated with a fragrant broth, while hủ tiếu appears in several regional preparations, including dry and soup versions. Pad Thai itself was popularized in Thailand in the mid-20th century, although rice noodles had much older Chinese roots.