en.wiktionary.orgon someone's back - Wiktionary, the free dictionary Contents From Wiktionary, the free dictionary Prepositional phrase[edit] on someone's back (informal) Nagging or harassing someone. My mother's been on my back about getting a job. Used other than figuratively or idiomatically: see on, someone's, back. on one's backon the back of Categories: English lemmasEnglish prepositional phrasesEnglish multiword termsEnglish informal termsEnglish terms with usage examples