A horse, especially a work horse or a child's word for a horse; sometimes spelled 'gee-gee' or 'gee gee.'
From the reduplication of 'gee,' the command word for horses, transferred to mean the animal itself. This is a playful, informal term popular in British English and children's speech.
Children's words for animals often come from the sounds humans make to control them—'geejee' literally comes from what you say to make a horse turn, showing how animal-command words become pet names.
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