gee-gee 
noun British informal
(In children’s use or in racehorse betting) a horse.Again however, the entire stake with the gee-gees is at risk....
- Still, he is curious about whether this choice of choo-choos over gee-gees was the right one.
- And he wants them to stop being so po-faced about gambling - a sin in which he enthusiastically indulges, at least when it involves gee-gees.
Origin
Mid 19th century (originally a child's word): reduplication of gee2.