So Bob Geldof wants to discover the nation's favourite word. Last week, launching the London International Literature Festival's millennium project, he announced that the hunt is on. Will he conduct polls and interviews? Are we talking oral or written language here? And aren't we all egotists whose favourite word is I?

There are moments, of course, when the ego dissolves. It is well known that people about to die, in extremis, often shout for Mum. So that's it then. Mum's the word. She sums up birth and death. We begin with her body, bawling for the breast, and in fantasy, in longing, we end there, too.

Freud certainly associated the image of the mother with the child's acquisition of speech. One of his stories concerns a small boy playing with a cotton reel on a length of string during his mother's temporary absence from the room. The child invented a push-pull game of gone-away and come-back. Mastering the cotton reel, the child simultaneously mastered words along with loss; loss is the mother of invention.

If Mum seems too obvious, too easy, how about fucking? That's the one you'll hear in the street, used for decoration and emphasis, for rhythm, for weighing and pacing sentences, repeated like a mantra until it becomes almost abstract, emptied of content. Perhaps men use this word more than women do, so let's hope Geldof's sample is equally composed of males and females.

But not only do men use words differently; different words are applied to men and to women. Let's stay with the letter F. Such lovely words begin with F - fantasy, furbelows, Flaubert, flow, flourish, feminism, flan. F is certainly for fashion. Favourite formats flicker, fast-forward and frequently fade following fickle fashion.

But there is another F word that is as ubiquitous as it is loathed: feisty. Feisty inhabits the worlds of journalism and novel-blurbs. You will not hear it applied to men. Only females are feisty. More specifically, feistiness belongs to heroines. Feisty is not witchy or bitchy. Like charity, it envieth not.

If you slung it in a poem and looked for half-rhymes, you might team feisty with fists, yeast, busty, fast. Feisty isn't really poetic, though. Feisty belongs and capers in prose. In gushy, romantic, deceiving prose. It is ostensibly praising, complimentary. It invokes a certain kind of womanly strength. It does what lusty or gutsy used to do for gels. Think Wife of Bath and Merry Wives of Windsor. Think pantomime dame with arms akimbo and ballooning crinoline. Think Angela Carter's mockery of thigh-slapping baroque.

You start to get a sense of ambiguity, ambivalence, of a put-down lurking just underneath the surface. A whiff of fakery or monstrosity. So why do people use the word so much? Perhaps it hints at the dilemmas of heroines in what is supposed to be a post-feminist world. Since we are constantly instructed that we must not be victims and must not whinge, we accept that we must be cheerful and brave at all times, like Girl Guides. Feisty. Not being over-sensitive and bursting into tears, but not turning into harridans, either.

Perhaps feistiness is the required condition of modern woman. An impossible balancing act. Damned if you do and damned if you don't. Battling against the odds, trying to bend the rules, or even to discover what these are in the first place, are we just tilting at windmills? Do we look faintly comic to observers?

Then feisty becomes also, perhaps, a term for a woman who doesn't know how to be properly feminine. Feisty is not fragrant. Fragrant is the opposite of smelly and, as we've learned from the law courts, of promiscuous. Whores, as long as they are golden-hearted and in the right kind of romantic or historical novel, might aspire, at the most, to become feisty. Virtuous wives, we know from a judge's immortal words, are simply fragrant. Cleanliness is godliness in this view, whereas sex stinks. But opposites attract and fragrance is drawn ineluctably towards stinkiness. Think of all those lavatory sprays fragranced with lemon and lavender. If forced to choose between fragrant and feisty, I'll plump for female every time.

• The Looking Glass by Michèle Roberts is published by Little, Brown on May 25 at £15.99.