The verb belittle means to dismiss as unimportant. Composed of the prefix be- and the adjective little, it means, literally, to make little—cf. also, for example, the verb bedim, meaning to make dim.

Thomas Jefferson (1743-1826), one of the Founding Fathers of the Constitution of the United States of America, coined belittle, and used it in its literal sense, in Notes on the State of Virginia, first published in Paris in 1785:

     (1794 edition)
Before we condemn the Indians of this continent as wanting genius, we must consider that letters have not yet been introduced among them. Were we to compare them in their present state with the Europeans, North of the Alps, when the Roman arms and arts first crossed those mountains, the comparison would be unequal, because, at that time, those parts of Europe were swarming with numbers; because numbers produce emulation, and multiply the chances of improvement, and one improvement begets another. Yet I may safely ask, how many good poets, how many able mathematicians, how many great inventors in arts or sciences, had Europe, North of the Alps, then produced? And it was sixteen centuries after this before a Newton could be formed. I do not mean to deny, that there are varieties in the race of man, distinguished by their powers both of body and mind. I believe there are, as I see to be the case in the races of other animals. I only mean to suggest a doubt, whether the bulk and faculties of animals depend on the side of the Atlantic on which their food happens to grow, or which furnishes the elements of which they are compounded? Whether nature has enlisted herself as a Cis or Trans-Atlantic partisan? I am induced to suspect, there has been more eloquence than sound reasoning displayed in support of this theory; that it is one of those cases where the judgment has been seduced by a glowing pen: and whilst I render every tribute of honour and esteem to the celebrated zoologist [see note 1], who has added, and is still adding, so many precious things to the treasures of science, I must doubt whether in this instance he has not cherished error also, by lending her for a moment his vivid imagination and bewitching language.
So far the Count de Buffon [see note 1] has carried this new theory of the tendency of nature to belittle her productions on this side the Atlantic. Its application to the race of whites, transplanted from Europe, remained for the Abbé Raynal [see note 2].
On doit etre etonné (he says) que l’Amerique n’ait pas encore produit un bon poëte, un habile mathematicien, un homme de genie dans un seul art, ou une seule science.

When Notes on the State of Virginia was published in London in 1787, The European Magazine, and London Review (London) of August published a review in which the anonymous critic expressed his anger at encountering belittle in the above-mentioned passage:

Belittle!—What an expression!—It may be an elegant one in Virginia, and even perfectly intelligible; but for our part, all we can do is, to guess at its meaning.—For shame, Mr. Jefferson!—Why, after trampling upon the honour of our country, and representing it as little better than a land of barbarism—why, we say, perpetually trample also upon the very grammar of our language, and make that appear as Gothic as, from your description, our manners are rude?—Freely, good sir, will we forgive all you attacks, impotent as they are illiberal, upon our national character; but for the future, spare—O spare, we beseech you, our mother-tongue!

The earliest known use of belittle in the sense to dismiss as unimportant is from The Better Sort: or, The Girl of Spirit. An operatical, comical farce (Boston, 1789), by the American author William Hill Brown (1765-93); one of the characters, Captain Flash, is described as being:

A British subject—one who loves to belittle America, and to talk about English politicks.

And the play itself contains the following dialogue:

– Peter Lovemuch. Why Capt. Flash, you seem to object to things, merely because they are American.
– Captain Flash. Step forward a little into the room, where we may be by ourselves, and I will endeavour to convince you of the truth of my arguments.
– Peter Lovemuch. Sir, I am a true whig of ’75, and a staunch federalist of ’89—and if you persevere to belittle my country, you’ll anger me sorely.

Notes

1-: Georges-Louis Leclerc (1707-88), Comte de Buffon, was a French naturalist, author of Histoire Naturelle, which he began publishing in 1749.

2-: Jefferson is quoting the following from Histoire philosophique et politique des établissements et du commerce des Européens dans les deux Indes, first published in Amsterdam in 1770, and attributed to the French author Guillaume-Thomas Raynal (1713-96):

     (modernised spelling)
On doit être étonné que l’Amérique n’ait pas encore produit un bon poète, un habile mathématicien, un homme de génie dans un seul art, ou une seule science.
     translation:
One should be astonished that America has not yet produced one good poet, one able mathematician, one man of genius in a single art, or a single science.