na-adjective
Describes something in its earliest, simplest, or most basic stage of development, often with a nuance of being unsophisticated or unrefined. Can refer to technology, societies, methods, or ideas.
この地域には原始的な農法が残っている。
Primitive farming methods remain in this region.
彼の考え方は原始的だ。
His way of thinking is primitive.
From 原始 (げんし, 'origin, primitive') + 的 (てき, '-like, -ic'). The exact historical derivation is straightforward; 原始 itself is a Sino-Japanese compound.