Picture an English full name laid out on a line: the personal part comes first, the family part comes last. The first name is the front part — the piece that belongs to you alone, not to your relatives. Because it is the personal piece, using it is also a small social move: the moment two people start using each other's first names, the distance between them has .
可以想成一個畫面：英文的全名排成一行，個人的那一段在前，家族的那一段在後。first name 就是前面那一段——只屬於你一個人的名字，不是跟親戚共用的。也因為它是「私人的那一段」，拿出來叫別人就帶有一點關係上的訊號：兩個人開始互相叫 first name，距離通常就拉近了。
From the word’s history
Recorded in Middle English as firste name; by surface analysis simply first + name, the name written first in the line.
來源記載中古英語有 firste name 的說法，拆開就是 first（最前面）＋ name（名字）：寫全名時排在最前面的那個名字。名稱來自位置，而在英文的排法裡，最前面那一段剛好就是屬於個人的名字。
Wiktionary entry for first name, supplied in packet (source_ref kaikki:3f6f69a190036ae4:18376307:3286)