1. [n]  the Tai language of a Buddhist people living in the area of the Mekong River in Thailand and Laos
2. [n]  a member of a Buddhist people inhabiting the area of the Mekong River in Laos and Thailand and speaking the Lao language; related to the Thais
3. [adj]  of or relating to a member of the Buddhist people inhabiting the Mekong river in Laos and Thailand

LAO is a 3 letter word that starts with L.