He polished his shoes until they were shiny.
godan verb (-ku), transitive verb
refine; improve; hone; cultivate
Metaphorical polishing: improving a skill, art, or personal quality through practice or effort.
語学力を磨くために留学した。
I studied abroad to improve my language skills.
彼女は日々、料理の腕を磨いている。
She hones her cooking skills every day.