noun
one tenth; one hundredth; one percent; one tenth of a sun; one quarter ryō
Historical and technical unit of proportion. In modern contexts, often means 10% or 1%, depending on the field. The sun and ryō senses are archaic monetary/measurement uses.
この合金には金が一分含まれている。
This alloy contains one tenth gold.
江戸時代、一分は一両の四分の一だった。
In the Edo period, one bu was a quarter of a ryō.
割 is the modern standard for 'one tenth' (10%), while 一分 is more historical or technical.
分 is the base unit; 一分 is one unit of 分.
Compound of 一 (one) and 分 (part, portion). The reading ぶ is the older Chinese-derived unit reading.