fork in a road
岔 centers on a point where a path divides: a fork in a road. The idea is a single route splitting into separate directions.
岔 combines 分 (divide) and 山 (mountain), suggesting a mountain path that splits or forks. The exact historical development is uncertain, but the component combination is consistent with the meaning.
The top 分 means 'divide', and the bottom 山 is a mountain. Picture a mountain trail that divides into two paths: a fork in the road.
For タ, imagine standing at a fork in the road and tapping your foot, unsure which way to go: tap -> タ.
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