フク, そい, そえ
vice-, assistant, aide, duplicate, copy
JLPT2 G4 S11 F360
The relevant oracle bone form of 畐# is a depiction of an alcohol container with a bulging middle and of abundant capacity (compare 腹). 副 adds 刀 sword/knife → cut/divide abundant contents into half → *halve* → *assist* (← assist by cutting/dividing) → *complement*; *supplement*; *accompany*; *duplicate*; *secondary*; *assistant*; *vice-*.
[Full Kanji Etymology List]