1. A boundary or border that is fixed, inflexible, and does not allow for easy movement, trade, or interaction across it
The rigid frontier between the two countries prevented any cross-border commerce.
A fronteira rígida entre os dois países impediu qualquer comércio transfronteiriço.
2. In academic or intellectual contexts, a firm demarcation line that separates distinct fields, disciplines, or ideas with little overlap
Scientists challenged the rigid frontier between physics and chemistry.
Cientistas desafiaram a fronteira rígida entre física e química.