This is the 2593rd most frequent Japanese word.
強固
"Strong" or "firm."
In this sentence, "強固" describes the firmness or strength of will, indicating a strong determination.
彼の意志は強固でした。
His will was strong.
Here, "強固" is used in connection with a structure, describing its solidness and durability.
この橋は非常に強固に設計されています。
This bridge is designed to be extremely solid.
The term "強固" is applied to describe the solid and enduring nature of the relationship.