契
ケイ, ちぎ.る

pledge, promise, vow

JLPT1 G7 S9 F898

The top element# combines 丯 a depiction of a piece of wood or bone that has been cut through and thus separated from the remainder + 刀 sword/knife → cut and separate wood or bone into pieces in creating a pledge/vow, with each party retaining a piece. 契 adds 大 great → great *pledge*/*vow* created by the means described above → *promise*; *tally*; *match*. In derivative characters the top element of 契 is often written in the form seen for example in 絜, 齧 or 挈 (and the same for 契 itself, as in 楔 and 禊).

[Full Kanji Etymology List]