Here are some strong synonyms for "rigid":

1. Inflexible
2. Unyielding
3. Stiff
4. Unbending
5. Firm
6. Strict
7. Uncompromising
8. Fixed
9. Adamant
10. Intransigent

"Rigid" typically refers to something that is stiff, unable to bend, or resistant to change. It can describe physical objects that are hard and inflexible, or it can refer to attitudes, rules, or systems that are strict and unaccommodating123.

For example: "The company's inflexible policies made it difficult for employees to maintain a work-life balance."

"He maintained an unyielding stance on the issue, refusing to consider alternative viewpoints."

"The stiff fabric made the dress uncomfortable to wear for long periods."

When choosing a synonym, consider the specific context and connotation you want to convey, as some words may carry slightly different nuances or levels of intensity.