what is a 'censor' in the hierarchy?

In chinese, the rank of 'censor' is called Yushi 御史

Yushi Dafu 御史大夫 (often translated as "supreme censor") was considered the highest official in ancient China after the prime minister (the higher hierachy) whose role was to supervise the acts of all officials. This rank began during Qin dynasty and by Western Han period, its power is somewhat like a "Vice-Prime Minister".

There are other lower ranks of censors under Yushi Dafu such as Yushi Zhongcheng 御史中丞 (censor 2nd), Shiyushi 侍御史 (censor 3rd) ，Xiuyi Yushi 绣衣御史 etc.

deputy prime minister i sppose?
i've came across this rank 'chancellor' in one of d dramas and initially i thought censor and chancellor were actually d same..
or is it not?

I don't think so. The Censors had the responsibilities to "censor" other government officials even the Emperor himself!!! I don't think the Chancellor has that particular duty.

I find that the term "Chancellor" is pretty much interchangeable with "Prime Minister", if I'm not wrong.

Anyways, are you sure? I don't think that the duty of a censor would necessarily be that related to our interpretations of "censorship" today. I just never got that impression from records I've read. I'll defer to someone more learned on this though, as it's a term I've usually just come across and assumed as another high-ranking position without consideration for the nitty-gritty parts of their duties.

Perhaps in a case such as this you can look at the etymology of the character for censor and find a clue to its real meaning. Is that a direct translation? Or is it an English equivalent?

The Censors (Yushi) were the eyes and ears of the Emperor, given authority (and indeed, the duty) to report on, investigate, and impeach officials of any rank who committed misconduct or failed in their duties. That is different from our modern understanding of 'censor', and is perhaps closer to the terms 'inspector' or 'watchdog'. Censors were periodically sent on inspection tours into the provinces and prefectures, but normally the inspectorial work below the prefectural level was done by specialized Local Inspectors or Prefectural Inspectors (Duyou 督邮) who belonged to the Prefect's office.

The direct descendant of the imperial Censors is the Control Yuan of the Republic of China, which still functions in Taiwan: http://en.wikipedia.org/wiki/Control_Yuan

The translation of Yushi as 'Censor' is based on certain similarities with the Censors of the Roman Republic: http://en.wikipedia.org/wiki/Censor_(ancient_Rome)

Hi Yun

In ancient Rome there was a position of : Inspector of granaries . But instead with that as a cover, they were there to in secret report on on the misconduct of officials. We use the expression even today when we refer to a person with some other title or position is really there to do secret checking under cover.