Merriam Webster is adding these words to their dictionary:

-Americana (1841): genre of American music with roots in early folk and country music.

I was shocked that this wasn't in there already, so I looked it up. It WAS in there already, this new addition refers to music. So take a look at the 1841 and consider whether it took them that long to add the music reference, or was that when the more general meaning of the word (things typical of America) came into use. (More about this date thing later.)

- boomerang child (1988): young adult who returns to live at her family home, especially for financial reasons.

Note the politically-correct 'her.' Remember those attempts to come up with totally gender-neutral pronouns? What about 30-year olds (him and her) who return to live at the family home? Is 'yo-yo generation' in there already?

- bromance (2004): a close nonsexual friendship between men.

- continuous positive airway pressure (1975): abbreviated CPAP; a technique for relieving breathing problems (as those associated with sleep apnea or congestive heart failure) by pumping a steady flow of air through the nose to prevent the narrowing or collapse of air passages or to help the lungs to expand.

- cougar (1774): slang term for a middle-aged woman seeking a romantic relationship with a younger man.

Really? So we could be watching that travesty of history, the John Adams miniseries from HBO and they'd use the word 'cougar' and we'd all gasp at the huge historical gaffe and rush to the Internet, and find out this term has been around just a tad longer than our United States? Indeed. Go look at 'tweet' and help me decide if perhaps this meaning of 'cougar' really dates back to 1776, or is that when the word was first used to describe a large cat living in the mountains.

- crowdsourcing (2006): the practice of obtaining needed services, ideas or content by soliciting contributions from a large group of people, especially from the online community, rather than from traditional employees or suppliers.

- duathlon (1988): a three-part long-distance race typically having a running phase, a bicycling phase and a final running phase.

I've never heard this word, but I'm not a runner, either, so no big surprise.

- fist bump (1996): a gesture in which two people bump their fists together, as in greeting or celebration.

What about 'fist pump?' Is that already in there. Is 'high five' already in there?

- helicopter parent (1989): a parent who is overly involved in the life of his or her child.

Is 'stage mother' in there?

- m-commerce (1997): business transactions conducted by using a mobile electronic device, such as a cellphone.

Do you remember the early cell phones? They were the size of a shoe, a good-sized adult shoe, not a little tiny baby shoe. And the people who had them got them through work self-consciously lugged those things around while co-workers eyed them and considered whether they were really all that important to deserve such a perk.

- parkour (2002): the sport of traversing environmental obstacles by running, climbing or leaping rapidly and efficiently.

It sounds more like 'parking (stopping)' than something relating to motion.

Here. I'll save you looking it up in Wikipedia:
"Parkour (sometimes abbreviated PK) is a method to overcome obstacles with speed, efficiency, and agility. Originally developed in France, the main purpose of the discipline is to teach participants how to adapt their movements to their environment by vaulting, rolling, running, climbing and jumping. Traceurs (parkour practitioners) train to be able to identify and utilize alternate or more efficient paths.

Parkour can be practiced anywhere, but areas dense with obstacles offer many different training opportunities. Parkour is often confused with free running. They are often used interchangeably even though these terms refer to distinct disciplines. Free running employs creativity through the use of tricking moves such as aerial rotations and spins."

Be sure not to call it free running.

- robocall (1993): a telephone call from an automated source that delivers a pre-recorded message to a large number of people.

Get ready for lots of these from now until after the next Presidential election. The bastards. I'm still bitter about politicians exempting themselves from the do-not-call regulations.

- social media (2004): forms of electronic communication, such as websites for social networking and microblogging, through which users create online communities to share information, ideas, personal message and other content such as videos.

- tweet (1768): a post made on the Twitter online message service.

Oops! There goes the credibility of this date-the-word-was-first-used-in-this-context business. There is no way in hell, no effing way the word 'tweet' back in 1768 had anything to do with online messaging. Oh, I just hate sloppy journalism like this. Now go back up there to 'cougar' and contemplate the possibility that in 1776 it could mean older women chasing younger men.

- walk-off (1990): ending a baseball game immediately by causing the winning run to score for the home team in the bottom of the last inning, i.e., a walk-off homer. Also, won by the home team in the bottom of the last inning, i.e., a walk-off win.