Definition of have (got) something on the brain in US English:

have (got) something on the brain

phrase

informal
  • Be obsessed with something.

    ‘John has cars on the brain’
    • ‘I have taken to shuffling about on the carpet with my rubber-soled shoes, distributing electric shocks because unlike the boys I don't have balls on the brain and rolling mouse balls along the carpet at a pin just doesn't interest me.’
    • ‘Peers and MPs had trains on the brain this week: the beloved Flying Scotsman, its clapped-out modern day equivalents which are, apparently, too small for fat people and those with broken-down loos.’
    • ‘I've had interviews on the brain for the past few months - verbal ones, written ones, for business and for pleasure.’
    • ‘I have a patient on the brain as well.’
    • ‘The Core Team, as you probably know, has babies on the brain.’
    • ‘For most of my adult life I have had a tune on the brain.’
    • ‘‘I have titrations on the brain,’ I gasped, nosily sucking in air.’
    • ‘Again I thought of Andreios, just a brief second, but the hair and appearance was again off (I really had guys on the brain, needed to get over this).’
    • ‘Or at least acknowledge that they have it on the brain as much as men do.’
    • ‘He had my children on the brain and made me feel like I was a total failure.’
    be fixated, be preoccupied, be infatuated, be possessed, be haunted, be consumed, be plagued, be tormented, be bedevilled, be eaten up, be gripped, be in the grip of, be dominated, be beset
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