We found one dictionary that defines the word standing on one's head:

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1. standing on one's head: Wiktionary

Definitions from Wiktionary (standing on one's head) ▸ adverb:  (informal, figuratively) Very easily. ▸ Words similar to standing on one's head ▸ Usage examples for standing on one's head ▸ Idioms related to standing on one's head ▸ Wikipedia articles (New!) ▸ Words that often appear near standing on one's head ▸ Rhymes of standing on one's head ▸ Invented words related to standing on one's head