Please wait here a moment; the doctor will be right with you.
Tips
usage
Two uses: a request, 'wait a moment', and a time word before the verb, 'in a moment, later': 等一下再说 'let's talk about it later'. A person waited for goes in the middle: 等我一下 'wait for me a second'.
register
Everyday and friendly. 等等 is just as casual; 稍等 and 请稍候 are the polite forms heard from shop staff and on the phone.