What is the definition for root word -tain?

The root word "-tain" is derived from the Latin word "tenēre" which means "to hold" or "to keep".

It appears in many English words and usually signifies the idea of:

* Holding or possessing something: "contain", "obtain", "retain".

* Maintaining or keeping something in a particular state: "sustain", "maintain".

* Being capable of holding or containing something: "certain", "mountain".

It's important to remember that the meaning of "-tain" can vary depending on the context of the word it's part of.