Sometimes word origins can be kind of mysterious. Take dilapidated, which derives from the Latin delapidare, which, as you rock hounds will have guessed, is based on the noun lapis, or stone. Hence lapis lazuli, a semi precious stone, and lapidary for someone skilled at working with precious stones. Lapidation is the term for punishment or death by stoning - and it says something about the modern world that the word doesn't yet have "[archaic]" beside it in the dictionary.
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But what does being in a state of disrepair have to do with small rocks? 

Nothing, unless you picture someone scattering stones every which way - which is what the verb delapidare means. It's a short hop from that image to the idea of a stone structure (a popular building choice among Latin-speaking builders and shopping mall developers) being gradually dismantled and its parts scattered by the elements until it is, literally, dilapidated.
 
For this reason, some diehards long maintained that dilapidated could only refer to stone structures (as opposed, say, to ageing bloggers). Let's be straight here and call such people what they are: crazy. They were demonstrating the etymological fallacy, which maintains that the "true" meaning of a word is its original meaning and nothing else. A more persistent example is the view that decimate can only mean reduce by a tenth, as it comes from the same root as decimal (base 10) and did, indeed, once mean reduce by a tenth. That was in the days when one form of discipline among army ranks or conquered hordes was to kill every tenth person to encourage the remaining nine to fall into line. (I know I would.)

But just as disciplinary practices evolve, so does language. Today decimate means kill, destroy or remove a large percentage of - the opposite, and way more brutal end of the spectrum from the original meaning. Genghis Khan would surely approve.