What is the etymology of "word!" [duplicate]

Question

Many people have begun to use the word "word" seemingly as an exclamation point or as a means to be emphatic.

Where and why did this begin?

Answer 1

Word!

Dig a bit deeper into the Urban Dictionary and you will find this:

word to your mother: An anachronistic corruption of the phrase "word to the mother", which was a popular reference to Africa or "The Motherland" during the late 1980s Afrocentric movement. While the replacement of "the" with "your" effectively obliterated the term's Afrocentric roots, it continued to be used in the same manner, that is, to express agreement. Alternatively, the "your" could take on sinister connotations, implying that speaker was sexually intimate with the listener's mother, as in "say hi to your mom for me", or, in keeping with the whack terminology, "props to your mom, she's da bomb". Finally, the phrase might mean nothing at all, and be used to ineptly feign street cred, in the style of Vanilla Ice.

FYI: Big Daddy Kane has a song "Word to the Mother(Land)," which you can hear here.

You will also find this explanation in Roc the Mic Right: The Language of Hip Hop Culture:

The African American oral tradition is rooted in a belief in the power of the Word. The African concept of Nommo, the Word, is believed to be the force of life itelf. To speak is to make something come into being. Once something is given the force of speech, it is binding—hence the familiar saying "Yo word is yo bond," which in today's Hip Hop Culture has become WORD IS BORN. The Hip Hop expressions WORD, WORD UP, WORD TO THE MOTHER, and similar phrases all stem from the value placed on speech. Creative, highly verbal talkers are valued.

This supports the comment from UD that it came from "my word is my bond," or a reasonable facsimile of the expression, but only in part. In 20th/21st century African American culture, "word" collocates broadly and creatively, and untangling its Genesis is a tricky business.

Answer 2

Are you referring to My word used as an exclamation, or expression of incredulity etc?

If so I am wondering why this comes with the suggestion that it is something new. I have heard it used all my life.

It is dealt with by the OED with examples since 1722.

my word (esp. as an exclamation) = upon my word at Phrases 1g(b)(ii).

Now chiefly as upon my word (also 'pon my word: see pon prep.). As an asseveration: assuredly, certainly, truly, indeed. In later use also as a simple exclamation of surprise or strong emotion. Now somewhat arch.

1722 A. Philips Briton ii. iii. 14 He loves thee, Gwendolen:—My word, he does.

1821 London Mag. June 658/2 When the New Town Christeners had exhausted their Georges and Charlottes and Fredericks and Hanovers, (and, my word, they did extend the royalty).

1841 E. C. Gaskell Lett. (1966) 44 My word! authorship brings them in a pretty penny.

1857 F. Locker London Lyrics 72 Half London was there, and, my word, there were few..But envied Lord Nigel's felicity.

1874 Trollope Harry Heathcote ii. 49 ‘You dropped the match by accident?’ ‘My word, no. Did it o' purpose to see.’

1932 P. Hamilton Siege of Pleasure in Twenty Thousand Streets under Sky (1935) ii. 62 ‘My word!’ said Violet. ‘You didn't half give me a turn.’

1960 C. Day Lewis Buried Day ii. 43 My word, how we did dress up in those days!

2004 G. Woodward I'll go to Bed at Noon xiii. 237 ‘That's an old Vincent,’ said Janus Brian, ‘my word. Haven't seen one of those for years’.