精一杯
せいいっぱい the best one can do; one's best effort
Why it means this
精 (energy) + 一杯 (a cupful — 'full') — with all one's might; the very best one can manage (精一杯やる).
Breakdown
- 精 セイ refined, ghost, fairy
- 一 イチ one, one radical (no.1)
- 杯 さかずき counter for cupfuls, wine glass, glass
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