ゆび
finger
yubi
JMdict 1309650
指(ゆび)fingerを切(き)りましたcut
I cut my finger
を (object) marks 指(ゆび) (finger) as what was acted on. The verb 切る(きる) (cut) is in polite past — built by taking the 〜ます (polite) stem and ending it with past 〜ました (did (polite)) — so it reports a completed action in a courteous tone.