crotch, thigh, groin, fork, junction, (kokuji)
俣 centers on a branching point where two parts meet: a fork in a road, a junction, or the crotch/groin area where the legs branch from the body. The thigh sense is closely related to that branching region.
俣 is a kokuji (Japanese-made kanji) combining 亻 (person) with 吴, which likely contributes the sound また and the idea of a fork or branching point. The exact historical development is uncertain.
A person 亻 standing at a fork 吴: the right side looks like a branching path, and the person marks the junction where the legs split.
For また, imagine a person at a fork in the road, and a friend calls out 'Mata!' (また, 'again') because they keep returning to the same junction.
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