Where words and phrases come from is a fascinating subject, full of folklore and historical lessons (continuing phrases beginning with F)

Fit (or fill) the bill - meet the requirements

Origin: Bill here means poster, as it often does (eg: billboard). The whole expression originated in America, where a famous performer whose name appeared in large letters on a theatre-bill to the exclusion of all others literally 'filled' the bill. The meaning (originally, 'have importance') shifted over the years, as frequently happens, as the phrase moved from theatrical circles that understood its origins to a wider public which did not.

Fingers crossed - hoping for luck or a happy outcome

Origin: Crossing one's fingers is a quick and easy way of making the sign of the cross to shield oneself from diabolic powers. It is also easy to keep them crossed, thus ensuring lasting protection from the devil's tricks.

Firing on all cylinders - working or operating at full strength

Origin: Literally (of an internal combustion engine) having all its cylinders working and thus providing the maximum amount of power. For example, the factory is firing on all cylinders to finish the orders on time

First-rate - of the best quality

Origin: Warships used to be classified according to six divisions called 'rates', in the sense of kinds or sorts, depending on the number of guns they carried. A ship 'of the first rate' belonged to the highest of these divisions and was therefore among the most powerful. This phrase became shorter as it passed from naval into general use.

Fit as a fiddle - in very good health

Origin: Fit has had this sense of 'in good condition' only since the 19th Century. Earlier it meant only 'convenient, right and proper'. One can only guess why a fiddle was thought to be particularly fit in this sense - perhaps because it was a piece of skilled craftsmanship and therefore to be admired, or because it's playing required dexterity. People used to say that a person who was liked had a face 'made of a fiddle' - they meant that it was always wreathed in smiles, as a fiddle has a much-curled shape. The origins of the modern expression probably lie somewhere among these associations.

Flavour of the month - something temporarily in fashion or popularity

Origin: American ice cream parlours, certainly by the 1950s, encouraged their customers to eat more (by lowering the price in a promotion) and try new flavours (by featuring a less known one) with a flavour of the month. This has been a widespread marketing ploy in recent decades in many fields.

Flea in one's ear, (get) a - receive a verbal rebuke

Origin: From the discomfort experienced by animals, especially dogs and cats scratching themselves to relieve the irritation of fleas biting or moving inside their ears. There is an obvious metaphorical link between the unpleasantness of such a nuisance and that of a word or rebuke in a person's ear.