to rub or brush an object to make it shine, especially a metal or wooden object

Robert was polishing up some old silver candlesticks. 罗伯特在擦拭一些旧的银质烛台。

to improve a skill, especially when you have allowed it to become less good over a period of time

I really must polish up my Japanese before we visit Japan next year. 明年我们去日本前，我真得恶补一下我的日语。