To dob someone in is to inform on them, usually to the police, a boss, a teacher or some other figure of authority. It carries a strong whiff of disloyalty, and calling someone a “dobber” is rarely a compliment. The phrase turns up in ordinary conversation as well as in more formal settings; a 1998 Victorian court judgment, for instance, records that a deceased man had “dobbed him in” to the police over drug involvement, showing the phrase used quite naturally in a legal context. A related but separate use has “dob in” meaning to chip in money towards a shared cost or gift, as in an account from 1968 of people who “dobbed in” for a fridge as a present, rather than betraying anyone at all.
What’s the origin of the phrase ‘dob in’?
“Dob in” is Australian in origin, and its root, the verb “dob”, is harder to pin down than the phrase’s everyday meaning suggests. The Australian National Dictionary Centre proposes that “dob” is probably related to a British dialect verb meaning to put something down heavily or clumsily, or to throw it, including throwing at a mark in games of marbles. On that theory, dobbing someone in would originally have carried something of the sense of dumping a problem, or a person, onto someone else, or hitting a target the way a well-aimed marble does.
There is a problem with that tidy explanation, though. The Australian National Dictionary Centre notes that “dob” is only first recorded in Australian English in the 1950s, far later than most genuine British-dialect borrowings into Australian speech. The lexicographer Bruce Moore has pointed out that the words and meanings known for certain to come from British dialect tend to appear in Australian English during the second half of the nineteenth century, not as late as the mid-twentieth. That gap leaves the dialect theory unproven rather than disproved, and the true origin of “dob” and “dob in” remains unsettled. What is clear is that by the 1950s Australians had a single, compact verb for informing on someone, and it has stayed in everyday use ever since, spreading well beyond Australia through general use in English.