Hot answers tagged etymology
Yes, many Japanese wonder why, too. The truth is that it's an obsolete usage of 天地 (except in this idiom!). 日本国語大辞典 (kind of the OED of Japanese) apparently has a definition: てん‐ち 【天地】 (...) (6)（─する）上下をひっくりかえすこと。 ＊滑稽本・早変胸機関〔１８１０〕「裾廻しは天地（テンチ）するだよ」 that is, 天地 once meant for "to turn upside down", at least attested on 1810 in Edo ...
This refers to the phenomenon of "Girl Power." Suggested search phrase: "girl power spice girls tattoo." One of the Spice Girls had a tattoo that was constructed of the kanji you describe. It is not a Japanese word, but an attempt to use kanji to write the English phrase "Girl Power." No difference in meaning whether written horizontally or vertically.
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