Yes, I would say that the use of morbid to mean pathological is more technical and old-fashioned than how we tend to use it today. I did a quick google search of that meaning, and it came up with a number of medical journals from the 1800's. That said, pathological is certainly still a synonym according to the dictionary. So, I'd say your sentence shows a correct, but not very common, usuage. In American English, at least, what Charles Han said above about how we use the word seems about right.

In the example cited above, it does not sound correct to say ""the child had a morbid propensity to tell lies", whereas your default, " "the child had a pathological propensity to tell lies?", is correct. We have a term called, "a pathological liar", and your default phrase would be readily understood. We do use "morbid" in the following contexts : 1) "morbidly obese" (to imply a condition to a degree that can illicit serious disease or death) 2) morbid curiosity (imply an unnatural fascination of death and situations surrounding death) A person with "morbid curiosity" hangs around the site of major car accidents or disasters. Also, one might describe a certain environment to have "a morbid ambiance", and describe as "morbid" various situations, like a scene in a movie.

The word "morbid" doesn't sound too technical nor old-fashioned. I would say it is commonly used in conversation. Also, while "morbid" could imply something pathological (in terms of a serious physical disease), the current use seem to focus on the sentiments of death. I do not see that it could describe a psychological pathology (except to say something like, "he had very morbid thoughts).