Sometimes in the tall grass of your text you will find – or insert – subtle interruptions, like panthers gliding through, making momentary disturbance and then leaving all as before: places where the author may slip little side theses between pairs of parabolas to set them apart from the parent clause. Asides, in short.
A parenthesis is an aside: it is something put in beside. The word parenthesis was assembled in Greek from παρα para ‘beside, around’, ἐν en ‘in’, and θέσις thesis ‘placing’. Originally, parenthesis (singular) refers to the aside itself, the text that is indicate by a shift in vocal tone, a turning away of the head, a setting apart in the text, before a return to the tone, position, or flow as before. When the practice came about of setting it apart with these curves ( ), the entire assemblage was first called a parenthesis, but since the bumpers travelled in pairs it just made sense, ultimately, to refer to them in the plural. And the plural in this case is a Greek-derived plural: just as we say theses rather than thesises, we say parentheses.
Or you could just call them panthers if you think you could get away with it. They do have that sleek, sometimes predatory nature. Allow me to cover parentheses in greater depth with a poem from my book Songs of Love and Grammar (available at lulu.com or amazon.com; also available as an ebook from the same sites).
Parentheses: cradled hands holding your message,
neatly bestowing a soft little blessage
(so much more peaceful than the visual rackets
that may be created by using square brackets).
They’re a velvet ink bag to soften hard words
(or a little surprise gift, loaded with turds).
Say your friend (a co-worker) sends you an email
suggesting (or foisting) an unattached female –
a little blind date (or myopic at best)
who’s eager to meet you (or willing when pressed).
Are you free (it’s been set up) on Friday at 9?
You can meet (if she shows) at the Savoy to dine.
She’s heard all about you (it goes without saying)
and she says you sound nice (she’s been told that you’re paying).
So you put on your suit (Goodwill, $10.98)
and comb down your hair (not much work) for your date.
She’s awaiting, with perfume (or bug spray) anointed,
and she seems quite demure (probably disappointed).
You order some drinks (loosen up things a notch);
her tastes are refined (she takes single-malt Scotch).
You make conversation (one word at a time);
you find she’s quite eloquent (just like a mime).
You think that she’s pretty (the drink’s kicking in),
and she smiles dreamily (she has moved on to gin).
The food comes (at last) and it’s simply divine
(like food offered to gods – burnt and sprinkled with wine).
Your date has filet mignon (charcoal briquette);
you went for the chicken (to stay out of debt).
For dessert, it’s Napoleon (from water loo)
and the chef’s special (leftover) tiramisù.
The mood is romantic: you look in her eyes
(or, anyway, somewhere ’twixt forehead and thighs).
You feel that she’s warmed to you during the meal
(it’s the closeness that comes from a mutual ordeal).
You call for the cheque and slap down your gold card
(two full meals and twelve drinks, tax and tip, damn that’s hard).
You offer to walk her home (can’t hurt to try);
she accepts (she’s afraid she’ll fall over, that’s why).
When you get to her door, you make as to kiss
but she blushes and turns (she’s afraid she would miss).
But the evening ends well – witness plans that you make
to talk in the morning (she’ll nudge you awake).
Ah, parentheses – they let you keep your composure
and charm (while still offering total disclosure).