Does เคย only mean "used to"?

It can also menas

- "ever" or "once"

- small sized shrimp for making shrimp paste (กะปิ).

Try: http://dict.longdo.com/search/%E0%B9%80%E0%B8%84%E0%B8%A2

I always thought เคย could express something that happened once, at some point in the past.

"เคย" = it can happened once or many times in the past.

"เคยชิน" or "คุ้นเคย" = familiar with; accustomed to; used to... Sometimes people just say "เคย".

The content of the sentence will help the listener to understand wheather "เคย" means

- it happend in the past, one or more times e.g. ฉันเคยไปฝรั่งเศษ

- it was a habits e.g. ฉันเคยขึ้นรถเมล์ตอนเป็นนักเรียน

For example, I thought the following would make sense:

เมื่อวานนี้ฉันเคย(ได้)กินอาหารไทย ("yesterday I ate Thai food". Happened once, at a specific point in the past: yesterday)

- "เมื่อวานนี้" indicated that it was in the past, "yesterday". Having "เคย" sound strange. You are talking specifically about the Thai food yesterday. "ได้" can be an option.

- If you want to say that you have ever ate Thai food before. You may want to say "ฉันเคยกินอาหารไทย".

- You may also consider using "ทาน / taan", a short for of "รับประทาน / ráp bprà-taan", for to eat. It will be more polite.

ฉันเคยดูภาพยนตร์นี้แล้ว ("I have seen this movie before". Happened once, at some unspecified point in the past)

- Correct. "นี้" indicated a particular movie.

But I read an article that said เคย is really only used to express an action that occurred either habitually, or over a long period, in the past. It is for something that you "used to do".

- "an action that occurred either habitually" should be "คุ้นเคย / kún koie" or "เคยชิน / koie chin" = be familiar ; acquaint

For example:

ฉันเคยกินเนื้อ แต่ตอนนี้เป็นมังสวิรัติ ("I used to eat meat, but now I'm vegetarian". An action that occurred habitually in the past)

- In this sentence "เคย" has a meaning of  "คุ้นเคย / kún koie" or "เคยชิน / koie chin". The person ate meat e.g. when was young. But if you want to say "I ate meat yeaterday.You should say "ฉันกินเนื้อเมื่อวานนี้".

ฉันเคยอยู่ที่เมืองไทย ("I used to live in Thailand". An action that occurred over a long period in the past)
- Correct.

Is the correct? Can เคย only be used to describe something that you "used to" do?

- However, "ฉันเคยไปฝรั่งเศษ" means "I used to visited France". One or more times.