[-线]

Jyutping seoi4 sin3
Pinyin chuí xiàn

Definitions (Wiktionary)
  1. noun
    perpendicular line; vertical line
Definitions (Kaifangcidian)
  1. (沒有對應漢語詞彙)

垂線 [-线]

Jyutping
Pinyin chuí xiàn

Definitions (CC-CEDICT)
  1. (math.) perpendicular line
  2. vertical line