1.
to settle down, to commit seriously to a task
To approach something with serious, sustained effort; to buckle down and work diligently.
腰を据えてやろう。
Let's buckle down and do this.
Instead of constantly changing jobs, why don't you settle down and work hard at one company?
2.
to settle in a place, to stay put
To establish oneself in a location for a considerable time.
I had been moving around overseas, but decided to settle down in my hometown.
Since we had a baby, we decided to stop moving and settle down in our current town.
Structure: 腰 (waist, hips) + を + 据える (to set firmly in place) — literally 'to set one's hips down', the image of sitting down properly to work instead of hovering.
Functions
1. Committing to a task: sustained, patient effort rather than dabbling. Very common in the て form before another verb — 腰を据えて取り組む, 腰を据えて勉強する.
2. Settling in a place: to stop moving around and stay put — a town, a company, a country.
Both share the sense of finally putting weight down in one spot after being unsettled.
OTHER 腰 EXPRESSIONS: