type 1; category 1; first class
Used as a prefix to classify something as the first type or category, often in technical, regulatory, or formal contexts.
I obtained a Type 1 electrician license.
This chemical falls under Class 1 designated chemical substances.
first-class mail
Compound of 第一 (first) and 種 (type, kind). The reading いっしゅ reflects a common sound change from いち + しゅ.