YOU ASK :
Where does the word Dada come from, and what does it mean?
Here's the simple explanation, straight from the horse's mouth:

from the Dada Manifesto
by Tristan Tzara
~ 1916

translation by Barbara Wright
but the following should be obvious, in whatever language:

To launch a manifesto you have to want: A. B. C., and fulminate against 1, 2, & 3, work yourself up and sharpen your wings to conquer and circulate lower and upper case A's, B's & C's, sign, shout, swear, organize prose into a form that is absolutely and irrefutably obvious, prove its ne plus ultra and maintain that novelty resembles life in the same way as the latest apparition of a harlot proves the essence of God.His existence had already been proved by the accordion, the landscape and soft words. To impose one's A. B. C. is only natural -- and therefore regrettable . . .

Dada -- this is a word that throws up ideas so that they can be shot down; every bourgeois is a little playwright, who invents different subjects and who, instead of situating suitable characters on the level of his own intelligence, lke chrysalises on chairs, tries to find causes or objects (according to whichever psychoanalytic method he practices)_ to give weight to his plot, a talking and self-defining story.

Every spectator is a plotter, if he tries to explain a word (to know!) From his padded refuge of serpentine complications, he allows his instincts to be manipulated. whence the sorrows of conjugal life.

To be plain: The amusement of redbellies in the mills of empty skulls.

If we consider it futile, and if we don't waste our time over a word that doesn't mean anything . . . The first thought that comes to these minds is of a bacteriological order: at least to discover its etymological, historical or psychological meaning. We read in the papers that the negroes of the Kroo race call the tail of a sacred cow: Dada. A cube, and a mother, in a certain region of Italy, are called: Dada. The word for hobby-horse, a children's nurse, a double affirmative in Russian and Rumanian, is also: Dada.

Some learned journalists see it as an art for babies, other jesuscallingthelittlechildrenuntohim saints see it as a return to an unemotional and noisy primitivism -- noisy and monotonous . . .

. . . thus Dada was born, out of a need for independence, out of mistrust for community. People who join us keep their freedom. We don't accept any theories. We've had enough of the cubist and futurist academies: laboratories of formal ideas. do we make art in order to earn money and keep the dear bourgeoisie happy? . . . here we are dropping our anchor in fertile ground.

EVERY PRODUCT OF DISGUST THAT IS CAPABLE OF BECOMING A NEGATION OF THE FAMILY IS Dada; protest with the fists of one's whole being in destructive action: Dada; acquaintance with all the means hitherto rejected by the sexual prudishness of easy compromise and good manners: Dada; abolition of logic, dance of those who are incapable of creation: Dada; every hierarchy and social equation established for values by our valets: Dada; every object, all objects, feelings and obscurities, every apparition and the precise shock of parallel lines, are means for the battle of: Dada; the abolition of memory: DADA; the abolition of archaeology: Dada; the abolition of prophets: Dada; the abolition of the future: Dada; the absolute and indisputable belief in every god that is an immediate product of spontaneity: Dada.

Dada Dada Dada; -- the roar of contorted pains, the interweaving of contraries and of all contradictions, freaks and irrelevancies: LIFE.

Tristan Tzara