na-adjective
specific; peculiar; characteristic
Used in technical or formal contexts to describe something that is distinctive or particular to a certain thing, often in contrast to 非特異的 (non-specific).
Antonyms: 非特異的
この症状はこの病気に特異的です。
This symptom is specific to this disease.
特異的な反
A specific reaction was observed.
Also means 'peculiar to' or 'characteristic of', but is a noun/no-adjective and more common in everyday language.
Compound of 特異 (tokui, 'unique' or 'peculiar') + 的 (-teki, adjectival suffix). The exact historical derivation is uncertain, but the word follows a common pattern for forming adjectival nouns from Sino-Japanese roots.