"My sister is pregnant."
Translation:Mia fratino estas graveda.
Both words came from outside of Esperanto and were not derived from each other by any of the internal rules of Esperanto. However, the words that they were based on do have an etymological connection (older than Latin.) Both "grava" (important) and "graveda" (pregnant) come from a root meaning heavy. (Yes, really.)
Older than Latin?
EtymOnline says for Latin:
Latin gravis, "heavy, ponderous, burdensome, loaded; pregnant;" of matters, "weighty, important;" of sounds, "deep, low, bass;" figuratively "oppressive, hard to bear, troublesome, grievous,"
implying that "heavy; important; pregnant" were all meanings of the same word in Latin, so we need not look for an etymological connection even further back.
That's what I get for only checking one resource. :-)
I was going from Cherpillod's KEV, which lists gravidus as the source for graveda.
Looking up "gravid", FWIW, says "Latin gravidus "loaded, full, swollen; pregnant with child," from gravis "burdened, heavy"
Maltese also uses "heavy" for "pregnant" - Jien tqila could be either "I'm pregnant" or "I'm heavy", though Jien tqil (with the masculine form of the adjective) would probably only get interpreted as the latter.
Li verŝajne pensas pri "grava" - grava domaĝo, serious damage ktp
"pity" is one meaning.
According to Krause, domaĝo is either "bedauerliche Sache" (regrettable thing = pity) or "Schaden, Nachteil" (damage, disadvantage), and PIV defines domaĝo as "Perdo aŭ difekto, kiun oni volus ne vidi, ne suferi".
And Krause says that damaĝo is "Schaden moralisch, auch materiell, vgl. dazu difekto u. dolo " (harm - moral or material; cf. difekto and dolo) while PIV defines it as "Malprofito kaŭzita al iu per ies agado".
So I'm not sure that domaĝo is wrong for "damage".
I note that Denisowski equates domagô = pity, something regrettable and damaĝo = damage.
So which dictionary is right?
I now see that the Universala Vortaro says "domaĝ' dommage | pity (it is a pity) | Schade (es ist) | жаль | szkoda."
So the Fundamento agrees with you - so I wonder where Krause and PIV get their idea of "Schaden / difekto" from.
Without digging too deep into all the quotations, my first reaction is that "schade" is most commonly used to mean "too bad", which lines up perfectly with "domaĝe".
We also have the biblical phrase "great with child" in English. Puts a positive spin on it.
If you're speaking to a human: not much.
Here on Duolingo: it's not one of the existing alternatives.
Remember that Duolingo doesn't understand Esperanto grammar -- it just checks answers against a predefined list of alternatives that are considered correct.
Since Esperanto word order is reasonably flexible, any given sentence can have a lot of possible answers, but entering them all takes up time that could better be spent fixing mistakes or adding "real" missing alternatives that don't just use unusual word order.
In general, stick to subject - verb - object word order here on Duolingo, as that is the most common word order in Esperanto and is the most likely to be in the database already.
Show that you understand how to make an Esperanto sentence by typing in Mia fratino graveda estas; showing how clever you are by choosing less common word orders is probably better reserved for conversations with humans.
Though even there, you might want to give them a miss -- the most common word order is the easiest to understand, so if your goal is to communicate (rather than to show how clever you are), use the wording that will cause the least amount of thinking necessary for your listeners, so that they can focus on the message rather than having to consciously think about the form of the message.
Speak like Yoda you can in English, understand you they will, but easier it is if ordinary word order you use.