What is the name of a verse consisting of 7 syllables? I thought it was caled a heptameter, but that seems to be something different.
I like chocolate cake with pears.
In English poetry, you only count syllables in haiku (a form borrowed from another language). Other languages, like French, count syllables in most forms of poetry. The reason is that English is a stress-timed language, and French is a syllable-timed language. This means that in English, the number of stressed syllables in a line is generally more important than the total number of syllables.
Seven-syllable lines in English verse can have several different names.
If you're trying to figure out the meter of a poem like Shakespeare's witches' chants, whose lines have the same pattern of stresses as your example:
Fillet of a fenny snake,
In the cauldron boil and bake;
Eye of newt and toe of frog,
Wool of bat and tongue of dog,
Adder's fork and blind-worm's sting,
Lizard's leg and howlet's wing,
this would be called catalectic trochaic tetrameter. (Catalectic because, compared with regular trochaic tetrameter, all the lines are missing a syllable at the end.)
On the other hand, the exact same pattern of stresses appears in the first line of Hughes Mearnes poem Antigonish:
Yesterday, upon the stair,
I met a man who wasn’t there
He wasn’t there again today
I wish, I wish he’d go away.
And here, it would be classified as headless iambic tetrameter, because the other lines are all iambic tetrameter.
And it's possible to have lines of seven syllables that are trimeter – for example, the 2nd and 4th lines from Tennyson's Break, Break, Break:
Break, break, break,
On thy cold gray stones, O Sea!
And I would that my tongue could utter
The thoughts that arise in me.
The feet in this poem are somewhat irregular, but it's classified as anapestic trimeter.