A year ago, UK citizens were told to “stay alert” in case Covid-19 crept up on them from behind. That having been such a success, we are now told that, with the new Indian variant threatening to derail plans to end the lockdown completely, we ought to be “vigilant”. What’s the difference?

In Latin, vigil means awake, and vigilare to stay awake. So a vigil, in English since the 14th century, is a period of watchfulness and concentration, originally religious (devotional rites, or a “wake” for the dead), but then potentially secular too. (As Alexander Pope described a crowd of scholars: “With studies pale, with midnight-vigils blind”.)

One who is “vigilant”, then, is both awake and concentrating, like a writer or a secret policeman, and so we have now been given a more arduous duty than simply staying “alert”. Beware, though, that in being vigilant you do not become a “vigilante”, the words being originally the same. As a Missouri newspaper of 1821 declared: “We hate what are called vigilant men; they are a set of suspicious, mean-spirited mortals, that dislike fun.” Happily at least, no less vigilant collection of people may be imagined than the present government.

• Steven Poole’s A Word for Every Day of the Year is published by Quercus.