Last Updated: July 20, 2020
This spreadsheet started life as a collection of vocabulary from the textbook used in my beginner Thai course at Chiang Mai University (Speak Thai in 15 Days). I have since added various sheets for different sources I came across during my self study. The two sheets for the course book are still here, but I now use a different sheet ('Vocab') to hold all the words I have studied from various sources (including online chat with Thai friends). The course book vocab is included as well so if you prefer to use that sheet you can ignore the Speak Thai in 15 Days sheets.

I have tried to be consistent in the way I add words, definitions and notes but you might occasionally see some inconsistencies. Generally speaking, I have used the Paiboon+ transliteration system, but while the CMU book is close to this system, there are some differences (e.g., ae vs. ɛɛ). I have tried to use the Paiboon system instead but probably missed some (many) words. You may also notice a few inconsistencies in transliterations for long and short vowels (e.g., nám and naám). Finally, note that words ending in either a G or K sound aren't fully pronounced in Thai so some transliteration systems use G and others K (e.g., bɔɔg vs. bɔɔk - to say). Mostly, I have used the K ending but there are probably some cases where I used G instead. Likewise with words ending in what can be either a D or a T sound.

The "Source" column is intended to list where I came across each word. It's probably not really very helpful in the end and most of the words that I picked up randomly are just marked "Extra." But, you could use it to differentiate any new words you add and/or to clean up some of mine.

For phrases and sentences, I have been quite inconsisten in using polite ending particles (krap, ka). Sometimes I use them, sometimes I don't. Sometimes I use one and sometimes I use both. If you are past the beginner stage, this shouldn't be an issue.
It's easy to accidentally add duplicate entries. On my latest update I tried to find and delete these. I may have missed a couple but I think I got most. For reference, if you want to search for duplicates yourself, check out:
With all that said, here's a rundown of the sheets you will find:
Vocab is my main collection of ~4,000 words and phrases.
Vocab (Priority) is a sheet that automatically shows only the "priority" entries from the Vocab sheet. It uses the Priority column so simply set that to Y for the words that are a learning priority for you. I personally use this sheet to generate vocabulary I want to import into Anki.
11 is a list of 1176 words which are considered some of the more commonly used words in the Thai language according to the site (one of my favorites). Source:
Speak Thai in 15 Days. This is the name of the book used at CMU. All the vocabulary on this sheet come directly from that book or from words covered in the classroom.
Speak Thai in 15 Days #2. This refers to the vocabulary picked up after we finished the first book in class. There is actually a second book in the series but often it covers the same vocabulary as the first book so the majority of words included here are from the classroom or from my experiences out of class.
Classifiers. This is not the complete list, but the more common ones. I have forgotten the original source.
Idioms. These were sourced from The Fundamentals of the Thai Language by Stuart Campbell and Chuan Shaweevong.
Ending Particles. This is really a work in progress that hasn’t progressed very far.
20 ใ words. Self-explanatory.