Did I miss something?

Why do you ask such a question?

Anyhow, here is what is says on Dictionary .com
plumb
–noun
1. a small mass of lead or other heavy material, as that suspended by a line and used to measure the depth of water or to ascertain a vertical line. Compare plumb line.
–adjective
2. true according to a plumb line; perpendicular.
3. Informal. downright or absolute.
–adverb
4. in a perpendicular or vertical direction.
5. exactly, precisely, or directly.
6. Informal. completely or absolutely: She was plumb mad. You're plumb right.
–verb (used with object)
7. to test or adjust by a plumb line.
8. to make vertical.
9. Shipbuilding. horn (def. 31).
10. to sound with or as with a plumb line.
11. to measure (depth) by sounding.
12. to examine closely in order to discover or understand: to plumb someone's thoughts.
13. to seal with lead.
14. to weight with lead.
15. to provide (a house, building, apartment, etc.) with plumbing.
–verb (used without object)
16. to work as a plumber.
—Idiom
17. out of or off plumb, not corresponding to the perpendicular; out of true.
plomb
–noun Surgery.
any inert material inserted into a body cavity for therapeutic purposes.