term for a grown child?

Y'know, someone should really put together a list of these things for which English doesn't have a useful word:

1. a third-person singular pronoun that refers to a person of either sex
2. a mature equivalent of "boyfriend" or "girlfriend" that neither implies too much or too little
3. the in-laws of one's in-laws
4. a plural of "only child", to simplify saying that neither of your parents had siblings
5. a parent whose child has died (we have "orphan" and "widow(er)" for similar roles)
6. an analogous term to "avuncular" for something that is "aunt-like"
7. a single bovine creature whose sex is unspecified (best I've heard offered is "cattlebeast")

Single bovine:

How about "beef"? I've run across references to X head of beef. Also Beeves.