Mother and Daughterboards
Long before what was to become the 1991 Gulf War was proclaimed as the "Mother of All Battles" by Saddam Hussein, the biggest circuit assembly in any PC was colloquially known as the motherboard. In a way, this circuit assembly is the "mother of all boards," but not in the way Hussein intended to refer to the pre-eminence of the expected engagement. Rather, the term hints at the function of the board and its relationship to boards that plug into it, which are termed daughterboards.
Drawing a direct analogy is fraught with strange images-you may imagine the smaller boards sucking from the larger one or the archaic concept of daughters clinging to their mother. Better to just think of the terms referring to the relative importance of the boards-mother is pre-eminent (mother knows best).
Spanish assigning the female gender to a table radio. (After all, sex and language gender are entirely different concepts, and anyone doubting that must have missed one of the more important high school health classes.) Besides, the term daughterboard is more mellifluous than alternatives such as "sonboard" or the more generic "offspringboard." The motherboard-daughterboard relationship has nothing to do with size. Just as daughters can grow up to be taller than their mothers, daughterboards can be larger than the motherboards they plug into.
In fact, the defining characteristic of the motherboard is not size or the circuitry it holds but the linkage it provides for expanding the system. Connectors rather than active circuitry are the essential elements of the mother-board. PCs can be (and have been) built with no components except expansion connectors and the electrical links between them on the motherboard.