In Star Trek: Deep Space Nine we find out that the Cardassian name for the Deep Space Nine space station is "Terok Nor." Later, the Maquis (in The Maquis, Part I) use a protomatter implosion device to destroy the Bok'Nor. Then in the episode Empok Nor we learn that there exists a twin station to Terok Nor called Empok Nor. My question is: do we know enough of the Cardassian language to know what this word means in Cardassian? Are there other instances of the Cardassians naming space craft or stations with the word "Nor"?
It likely refers to "mining".
It's true that the writers and producers have never explicitly defined the word "Nor", but there is evidence to suggest that it doesn't mean "station". (Note that the news group "dictionary" in rand al'thor's answer is just fan work.)
Both Terok Nor and Empok Nor were ore-refining facilities. As established in many DS9 episodes, including the pilot episode "Emissary", the Bajoran slave labourers were used to staff the uridium ore-refining facilities on Terok Nor.
The reason I believe that it refers to ore and/or mining rather than "station" is that in "The Maquis" episode, we have a Cardassian ship named the Bok'Nor, which is a mining vessel.
Since the only thing that the stations and the ship have in common is mining, I suspect "Nor" refers to mining or ore.
According to Memory Alpha, very little is known canonically about the Cardassian language other than some proper nouns such as names of people or places ... however:
Non-canon but canon-based
You may be interested in this short introduction and tutorial for the Cardassian language. It was written some 20 years ago by members of the newsgroup alt.startrek.creative, including Timothy Miller and Chris Pinette. While it has never (to my knowledge) been officially sanctioned by the Star Trek showrunners, it is based on the snippets of the Cardassian language seen on-screen. According to their vocabulary list, "nor" means "station".
Out of canon, 'Nor' refers to a space station class.
In the TNG novel 'The Battle of Betazed', there is reference
to a type of Cardassian-designed space station
In canon though, we don't have much information to go on. As rightly pointed out by TZHX, there is a Cardassian Bok'Nor type Freighter.
Yet, we do not know whether Empok Nor was ever used in industrial or mining processes, so we cannot necessarily conclude that 'Nor' refers to industrial or mining processes.
Because of the use of the term in both a freighter and a space station, I am inclined to believe that Nor (exclusively) does refer to a space station type. I would postulate that the designer of the space station, or perhaps the organisation which designed the Nor-type space stations, was called 'Nor' and the reference to it in the name of the freighter could be that another company/individual (probably of the name Bok) teamed up to designed the Bok'Nor type Freighters.
Terok Nor probably means space station number 9 and Empok Nor probably means space staion number 8 or 10.
A cardassian counting system would probably shed light on the matter.