In Russian language, 'invalid' term is applicable exactly to human beings and means the disabled human. I suppose it might be so in another languages, so there's question if the mentioned book was translated to English from another language.
Similar in general, but different in particularities meanings are typical for the words borrowed from another languages
F.ex.... 'hund' means 'a dog' in Norwegian, but 'hound' means the kind of dog in English
'Speculation' means something like pondering, contemplation, thinking in English, but in Russian it means only the buying something cheaper and sell expensive thus making the profit (it was reason to be jailed in Soviet times BTW :) ).
Origin is obviously the same but the usage survived for one particular meaning.
So for the word 'sympathy' has nothing common in its Russian analog with condolence, compassion - it means only something like attraction, appeal, affection.
And many another words which are borrowed tend to mutate in another languages acquiring slightly deviated meaning. Sometimes in the translated messages I noticed the misusing of such words when the interpreter translated it from English literally and it sounded off in Russian. I guess it might be a case for the discussed example as well.
5Maulik's answer is certainly correct, but the pronunciation difference is important so make sure you check out Chenmunka's answer as well. – Tyler James Young – 2014-04-17T14:03:38.443
I strongly suggest reading FumbleFinger's answer. It provides the most accurate and relevant information, with the more important details provided. Maulik's answer doesn't particularly detail out what an invalid is beyond being sick (it's not that simple). Chenmunka's answer also doesn't provide too much detail and what it does provide is potentially confusing and could lead to insult if a learner used 'invalid' to describe a person with just any disability (a person in a wheelchair, blind, etc is not an invalid, even though they are disabled/handicapped). – Doc – 2014-04-18T23:59:22.923
@Doc You can even add too much detail by go on explaining the etymology, justification of whether it should be PC/NONPC and so on. But The OP here simply asked, what invalid means here and he seems unaware of the basic definition. The basic question is How a person can be invalid (which I addressed it) and not Is calling a person 'invalid' morally okay?' (This I would have certainly explained thoroughly being a healthcare provider). And yes, I know this better than others because my mother is invalid since last year. – Maulik V – 2014-04-19T05:18:51.230
1@MaulikV I have no comment regarding morality or PC, but calling a blind person an invalid simply isn't the proper use of the word. Nor would a person with chronic back pain, Asthma, Diabetes, Epilepsy, HIV, etc - all of which are chronic illnesses that fall into your provided extremely oversimplified definition. Most injuries, even extremely serious ones that lead to amputation of multiple limbs would also not make a person an invalid (except maybe temporarily during early recovery). Those details are important to understanding the basic definition. – Doc – 2014-04-19T07:40:27.720
The film Gattaca uses the term in the nonconventional sense of "this person is not valid". I haven't seen it used this way anywhere else. – None – 2014-04-19T08:30:18.480