Character Dian

It means a summit, a fall, or something turned upside down.

An oracle-bone ancestor shows a person tumbling from a raised place. Bronze and seal forms recast it as 頁, head, plus 眞 for sound. Classical use extends that fall into jolting, inversion, and toppling.

Do not read a lone 顛 as crazy. That sense belongs to 癲/癫; 顛 appears there only as an older interchange. Read 顛倒 as reversal and 顛覆 as overturning.

Why do 顛, 顚, and 颠 differ?

They are standard forms of one character, not different words.

Traditional Chinese uses 顛; simplified Chinese uses 颠. Japanese print standard uses 顚 and treats 顛 as a variant, as in 顚末, the whole course of an affair. Korean Hanja reads it 전. Copy it from the palette above in the form your text uses.