1to fix; to set; to make definite
2to congeal; to coagulate
3(literary) definitely
4to subscribe to (a newspaper etc); to book (tickets etc); to order (goods etc)
Examples
tā他hěn很kuài快jiù就xià下dìng定le了jué xīn决心。
他很快就下定了决心。
He made up his mind quickly.
他下定了决心要做医生。
He made a determination to be a doctor.
她终于下定决心要出国了。
She finally made up her mind to go abroad.