If you think about it, abject ("miserable"), object ("thing"), inject ("to push into"), deject, ("depress") and reject ("dismiss") all share the same Latin root: what went into English as ject came from Latin as the verb iacere, which meant "to throw". It all makes perfect sense if you think about it. Ab- means "away from" (from the PIE root apo, "away"), and something miserable is meant to be thrown away. The same logic applies for deject: de- (of Etruscan origin) means "down" and you can definitely makes someone depressed by throwing them down figuratively. Re- (from PIE wret, "to turn") means "back", and throwing something back is the ultimate sign of rejection. When you inject something, you're pushing it in (yes, in- the prefix, which derives from PIE en, means "in", obviously), and it's only a bit of a stretch to say you're almost "throwing" it in. Object is the strangest of the five and has developed the most: ob- (from PIE opi, "against") was the Latin prefix for "against". Something against which stuff is thrown is a target, and a "target" was exactly what the original definition for object was; later it developed to mean "stuff" in general and singular. Now that we know all that, iacere is from the Proto-Italic word jajko, from Proto-Indo-European hyeh. Both terms meant "to throw". How interwoven our language is!
Adam Aleksic has been described as the internet's sixth most famous etymologist. He loves writing about himself in the third person, he's a freshman at Harvard University, and he has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law.
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