一いち大だい決けっ心しん

noun, noun or participle which takes 'suru'

momentous decision; crucial decision; big resolution

A yojijukugo used when someone makes a very important, life-changing decision or resolution. Often implies a dramatic, once-in-a-lifetime determination.

• 彼かれは一いち大だい決けっ心しんをして会かい社しゃを辞やめた。

  He made a momentous decision and quit his job.

• 留りゅう学がくするために一いち大だい決けっ心しんした。

  I made a big resolution to study abroad.