na-adjective
constant; invariable; chronic; everlasting
Describes a state or condition that is unchanging, persistent, or permanent. Often used in formal or technical contexts.
この地域では恒常的な水不足が問題になっている。
A constant water shortage is a problem in this region.
彼は恒常的なストレスに悩まされている。
He suffers from chronic stress.
一定 means 'fixed' or 'constant' in a more general sense, often implying a set standard or uniformity, whereas 恒常的 emphasizes an enduring, unchanging state over time.
Compound of 恒常 (kōjō, 'constancy') + 的 (-teki, '-like, -ic'). 恒常 is itself composed of 恒 (kō, 'constant') and 常 (jō, 'usual, ordinary').