I'm looking for an adjective which means "few people know" or "only professionals know".
Especially, I want to describe settlement & clearing fields as "__________ fields".
Here is a full sample sentence. "I needed to learn the business model of XXXXX (the name of company which provides clearing services). However, because settlement & clearing is a very _____ field, it was very difficult to research by myself."
I came up with a word "esoteric" and found other posts discussing this word, but I'm not quite sure this word can be applied to context above for the following two reasons. 1. I thought "esoteric" means something like very eccentric hobbies, not formal things. Therefore, if I refer to settlement & clearing as "esoteric fields", it may sound humorous. 2. I'm not sure how frequently this word is used by native speakers.