Pronunciation: [hav ˌɒn bɹˈe͡ɪn] (IPA) 
The phrase "have on brain" refers to having something constantly on one's mind. It is usually spelled this way in informal contexts, although it is not grammatically correct. The correct phrasing would be "have something on the brain." The pronunciation of the word "have" is /hæv/, while "on" is pronounced /ɒn/. "Brain" is pronounced as /breɪn/. When put together, the phrase is pronounced as /hæv ɒn breɪn/.
To have on brain is an idiomatic expression that refers to a person being preoccupied, obsessed, or constantly thinking about something or someone. This phrase is commonly used to describe a situation when a particular topic or concern is occupying an individual's thoughts and attention, often to the point of distraction or difficulty focusing on other tasks or conversations.
When someone has something on brain, their mind becomes fixated on that particular subject or issue. It can refer to a variety of things such as worries, concerns, or even hopes and dreams. It implies that the individual cannot stop thinking about the matter at hand and it continues to dominate their thoughts and mental space.
Having something on brain implies that the topic is continuously running through the person's mind, perhaps causing them to lose sleep or affecting their concentration on other activities. It may manifest as constant rumination, where the individual repeatedly goes over the same thoughts and ideas related to the matter, unable to let it go.
Overall, to have on brain refers to being mentally preoccupied or consumed by a specific subject, usually to the detriment of one's ability to focus on other things. It highlights the intrusive nature of the thought or concern and its capacity to dominate an individual's mental landscape.
