Depending on context, filler is a much more complicated concept. You could be referring to stuff they put in food that is not food, or stuff they put in cracks

Depending on context, filler is a much more complicated concept. You could be referring to stuff they put in food that is not food, or stuff they put in cracks to fill them in, or a nozzle at a gas station. By contrast, go is such a foundational word to English that it appears in English reading primers for toddlers, and a goer goes.