From Longman Dictionary of Contemporary Englishthe mother of somethingthe mother of somethinga) COME FROM/ORIGINATEthe origin or cause of something Westminster is known as ‘the mother of parliaments’. Necessity is the mother of invention (=people have good ideas when the situation makes it necessary). b) informalBAD a very severe or extreme type of something, usually something bad I woke up with the mother of all hangovers. → mother
Examples from the Corpusthe mother of something• the mother of all battles• Necessity is the mother of invention.• I woke up with the mother of all hangovers.