Elusive word and its meaning thereof...please help

[MagicalSilverKey]

I have been studying personality disorders, and the word comorbidity often arises in the texts thereof. I cannot find this word in any dictionary that I have looked in. (I have used almost a dozen, so far!) What does comorbidity mean? The following paragraph is an excerpt from one article about Avoidant Personality Disorder. I hope this helps in regards the context and usage of the word.

It is common for persons with AvPD to have comorbidity with other personality disorders. AvPD is most often diagnosed with DPD, BPD, PPD, SPD, or StPD (DSM-IV, 1994, p. 663). Frances, et.al (1995, p. 376) note the considerable overlap between AvPD and DPD. These two personality disorders share interpersonal insecurity, low self-esteem, and a strong desire for interpersonal relationships. Benjamin (1993, p.301) describes the desperate attempts to avoid being alone that may be seen in DPD as an exclusionary indicator for AvPD.

[SmackFu]

I found it by searching medical dictionaries. Here’s a quickie definition:

Comorbidity: The coexistence of two or more disease processes.

Here’s a page with a more involved one: http://www.graylab.ac.uk/cgi-bin/omd?comorbidity