This is the 573rd most frequent Persian word.
ثابت
Fixed; stable; constant.
In this sentence, 'ثابت' refers to being stable or unchanging, as in a steady state.
مدار الکتریکی باید ثابت باقی بماند.
The electrical circuit must remain stable.
Here, 'ثابت' indicates solidity or firmness as a characteristic of ideas.
ایدههای او بسیار ثابت و غیرقابل تغییرند.
His ideas are very firm and unchangeable.
In this context, 'ثابت' is part of the verb 'ثابت کردن' meaning to prove or establish.