(n.) a slight stinging pang of anguish or pain
In a letter written to his childhood friend Atticus sometime around 60BC, the Roman statesman Cicero lamented that he dearly missed long-time friend’s companionship.
Despite having a wife and a young family, and despite being surrounded by “troops of friends” and well-wishers on his journey down to the forum each morning, Cicero confessed that he missed having someone “with whom to jest freely,” or someone “into whose ear I can breathe a familiar sigh.” Not only that, but he missed having a friend and advisor around him, with whom he could share and discuss all of his worries and troubles:
I have many anxieties, many pressing cares, of which I think if I once had your ears to listen to me, I could unburden myself in the conversation of a single walk. And of my private anxieties, indeed, I shall conceal all the stings and vexations, and not trust them to this letter and an unknown letter-carrier. These, however—for I don't want you to be made too anxious—are not very painful: yet they are persistent and worrying, and are not put to rest by the advice or conversation of any friend.
Cicero’s letter, of course, was written in Latin—and it is the word that has been translated here as ‘stings’ that concerns us here. Aculeus was the Latin word for a stinging spine or prickle, derived from acus, the Latin for ‘needle’. In that original and somewhat literal sense it was used for everything from bee and wasp stings to rose thorns, the prickles and barbs found on spiny plants, and even the sharpened tips of arrows and darts.
But over time aculeus developed a more figurative use, and later came to be used of cutting or sardonic remarks, hurtful comments, and—as here in Cicero’s letter—any slight trouble or worry that causes mental, as much as physical, upset.
Adopted into English in the 1600s, aculeus is still predominantly used in its zoological and botanical senses, but this more figurative use nevertheless survives. So if you have a nagging, worrying thought or problem—the kind that you would dearly like to share with a friend—then that is an aculeus.