“What does “chichi” mean in Spanish slang?”
Depends on the country and sometimes a region within a country. Note that it can be found and used either as “chichi” or “chichí “ in the latter case with the accent on the second syllable.
In Argentina it typically means a young woman. Among other things.
In Bolivia and some other places it usually means your girlfriend
In Colombia it can mean something petty and disagreeable, or urine.
In the Dominican Republic, Honduras, Panama, some other places, it can mean a very young baby.
In Panamá, chichí —with accent on the second syllable — can mean a newborn or very young baby.
In Mexico and Perú and some other places it can mean tits. Under some circumstances in limited parts of Mexico it can mean grandmother or uncommonly, a nursemaid. Note that much of the region is affected by the indigenous Náhuatl language meaning of the word, which meant “to suckle.”
In Spain it’s vulgar and means cunt.
Probably a lot of other meaning as well.
Because Spanish isn’t the same everywhere you go.