So, I want to return to the conversation about nervous ticks and nervous tics. One might have a nervous tic when there are too many insects about, but a tick might be nervous if there is use of repellents/repellants.
But that begs the question:
How do you spell repellent/repellant? Repellant with an A? Repellent with an E?
Answer: “repellent”—with an “e.”
But before you confidently walk away from this “repellant” vs. “repellent” conundrum, let’s pause for a moment, because the other spelling isn’t completely incorrect.
What we have here is a case of preferred spelling versus accepted spelling. Both “repellant” and “repellent” are indeed words. Both have been used for over three hundred years. When I dug a bit deeper and looked into the Google Books Ngram Tool, it was confirmed that “repellent” is and almost always has been the more common spelling, with the exception of a strange outlier moment in history between 1722 and 1727 where “repellant” jumped ahead. What happened in these five years that almost but not quite changed the fate of this spelling, I have no clue.
“Repellent” and “repellant” trace back to the Latin word repellere, meaning to drive back. You can use insect repellent or have repellent behavior. I’d suggest being cautious with both, but at least you can feel confident in your spelling.