na-adjective
exclusive; exclusionary; cliquish
Describes groups, attitudes, or systems that shut others out; often carries a negative nuance of being unwelcoming or insular.
あのサークルは排他的で、新入りが入りにくい。
That circle is exclusive, making it hard for newcomers to join.
排他的な態度を取ると、友達を失うよ。
If you take an exclusionary attitude, you'll lose friends.
独占的 means monopolistic or exclusive in the sense of sole possession or control, often in business contexts, whereas 排他的 is about social exclusion.
Compound of 排他 (exclusion) + 的 (-like, -ive). 排他 is from 排 (push aside, exclude) and 他 (other).