该

gāi

should

ought to; probably; must be; to deserve; to owe; to be sb's turn to do sth; that; the above-mentioned

speech (讠) + sound [亥] = the word you ought to say

讠 carries the meaning: a word that must be said, an obligation spoken aloud. 亥 is purely phonetic, lending the gāi sound without semantic weight.

讠+亥→该

亥The last of the twelve earthly branchesPhonetic

讠SpeechSemantic

不该

bù gāi

should not

亚该亚

yà gāi yà

Achaia

合该

hé gāi

ought to; should

哈该书

hā gāi shū

Book of Haggai

应该

yīng gāi

ought to; should; must

应该的

yīng gāi de

(polite response) you're welcome; just doing my duty; no problem

撒都该人

sā dū gāi rén

Sadducees

活该

huó gāi

(coll.) serve sb right

米该亚

mǐ gāi yà

Micah

该亚

gāi yà

Gaea, the Earth Goddess and mother of the Titans

该博

gāi bó

erudite

该应

gāi yīng

should