• 先日せんじつ — the other day / a few days ago
• 先頭せんとう — front / head (of a line, group)
• 先行せんこう — precedence / going ahead
• 行いき先さき — destination
• 指先ゆびさき — fingertips
• 先輩せんぱい — senior / upperclassman

先生せんせい — this word literally means “one who was born before” or “one who came ahead,” highlighting the respectful notion of someone with prior experience or knowledge.

“先” expresses both direction and order — whether someone walks ahead, speaks first, or has greater experience.

先さきに 行いってください。
Please go ahead.

先せん生せいは 英語えいごの 先せん輩ぱいです。
The teacher is a senior in English studies.