na-adjective
Used in legal or political contexts to describe something that is in accordance with the constitution. Often appears in formal writing or discussions about laws and government actions.
その法律は合憲的だと最高裁が判断した。
The Supreme Court ruled that the law is constitutional.
合憲的な
We must resolve the issue through constitutional means.
違憲的 means 'unconstitutional', the opposite of 合憲的. Both are adjectival nouns used in similar formal contexts.
Compound of 合憲 (ごうけん, 'constitutional') + 的 (てき, '-like, -al'). 合憲 is itself from 合 (conform) + 憲 (constitution).