noun
first impression; immediate thought
Refers to the very first thought or feeling that comes to mind upon encountering something or someone.
彼に会った第一感は、とても誠実そうだということだった。
My first impression upon meeting him was that he seemed very sincere.
この企画を聞いた第一感は「面白そう」だった。
My immediate thought when I heard about this project was 'That sounds interesting.'
直感 is 'intuition' or a gut feeling, often without conscious reasoning. 第一感 is more about the initial thought or impression, which may or may not be intuitive.
Compound of 第一 (first) and 感 (feeling, sense).