Four-letter words fly under the radar, deceiving us into thinking that they aren’t all that important. But these words that are short on letters can be long on meaning.
In English, certain words are reserved for solemn, formal occasions. “Aver” comes to us from the courtroom and means to attest or declare, e.g., the defendant averred that he was nowhere near the scene of the crime. More broadly speaking, “aver” can be used to describe an intellectual person who is making a firm statement, e.g. Most scientists studying climate change aver that we must make significant change in global emission lest irreparable damage is done to the earth.
From the Latin for cross, the crux is the most essential or important point of an issue. The crux of climate change (to invoke that example, yet again) is that the Earth is changing so much that we might not be able to undo the damage. A good way of thinking about crux is that it is the heart of the matter, the most essential point.
A ruse is a clever trick or scheme. People who are spies live lives that are a complete ruse. They pretend to be somebody who they aren’t and make friends with the very people who are their enemies. Of course, pulling a ruse need not be that sinister; when I proposed to my wife, I pretended that we were going on an average road trip, describing the hotel I had apparently booked a few hours out of town. Instead, I drove to the airport where we boarded a plane to Central America, where, in the middle of a beautiful lake, I asked her to marry me.
This word does not relate to locomotives, at least the meaning I’m referring to here. To rail against somebody is to criticize that person bitterly. Of course you don’t have to rail against a specific person; you can also rail against the government or practices you find abhorrent. Hopefully, you don’t find yourself railing against the vocabulary that you are forced to learn for the GRE.
Whether it appears as an adjective or a noun this word is all about wisdom. A sage (n.) is a deeply wise man. The word has an old time-y connotation, conjuring up Biblical prophets with beards down to their ankles. Sage as an adjective generally applies to anyone or anything displaying wisdom. No long beards required.
The meaning I’m drawing on here is similar to despicable. To describe somebody’s motives as “base” means that person is ignoble and has no sense of moral scruples. Were somebody whom you consider a friend to spread malicious lies about you, just to make themselves look good, you’d consider their behavior base.