Different word about Back and spine

Question

I've seen many different words refering to back, spine like せ and せなか. So what is the right word and in which case?

Answer 1

In modern Japanese, せなか is the usual word for "back", but it comes from the old word せ which also means "back", or "a raised portion" and which occurs in other contexts:

• [背が高い]{せがたかい} means "tall" (Here's a discussion about whether to read it せがたかい or せいがたかい: http://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1411676039)
• [背番号]{せばんごう} means the number on the back of a sports player

See also the entry for 背 at Wiktionary: https://en.wiktionary.org/wiki/%E8%83%8C