最普通的说法是 to urinate(名词是 urination),如果去看病,护士为了化验小便,就会给你一个杯子说:「Will (could) you urinate in this cup?」医生或许也会问:「Do you have trouble urinating?」=Do you have difficulty voiding?(小便有困难吗?)
此外,还有其他的说法:to piss = to take a piss = to take a leak = to void = to empty。 例如:
I need to piss = I have to take a leak.
How often do you get up at night to void?(晚上起床小便几次?)