I'm really not trying to pick a fight, this is an honest question...

What is the precise medical definition of "depressed"?
The only free online dictionary I found, Merriam-Webster, lists:

1. a state of feeling sad
2. a psychoneurotic or psychotic disorder marked especially by sadness, inactivity, difficulty in thinking and concentration, a significant increase or decrease in appetite and time spent sleeping, feelings of dejection and hopelessness, and sometimes suicidal tendencies.

(As well as some others, referring to indentations in glass, and whatnot...) Then again, I didn't check a medical dictionary. People seem very sensitive about the distinction... is it incorrect or insensitive to use the word to imply the first definition, above? It seems like a qualitative distiction, given that there is no real litmus test. Or is there?
Thanks