This is the Navajo word for ‘lightning’ (also sometimes written as ‘atsinil-tlish). It’s also the word used for ‘electricity.’
The ‘tłish’ part is most likely referring to a sound, such as a loud clap (or, you can imagine a metal pot falling onto the hard floor).
1. they say
"They say. When you say they say, you are just making it up, they say. So that's why you do not say they say, they say."
2. it is said, it was said
3. 4th-person singular imperfective of ní
Literally: it is good (alternatively: it is well).
This is considered the Navajo ‘hello,’ so it can be used to greet people.
It can also be used with ‘shił’ as in ‘shił yá’át’ééh’ to mean ‘I like it.’
In English, it’s part of a verb group that means “to be named” or “to be called.”
For example, if my name were Fenton I would introduce myself like this: “Yá’át’ééh, shí éí Fenton yinishyé.”