1. verb To strike someone or something repeatedly. Quit hammering on your little brother, Billy! Who's hammering on the front door at this ungodly hour?

2. verb To secure something onto something else by striking it repeatedly (not necessarily with an actual hammer). In this usage, a noun or pronoun can be used between "hammer" and "on." We need to hammer on this board now.

3. verb When playing a stringed instrument (typically a guitar), to pick a note and then bring one's finger down upon another note on the fingerboard, in order to change the original note. In this usage, the phrase is usually hyphenated. Hammer-on that note—it'll sound better.

4. noun The act of doing this with the fingers while playing a stringed instrument. In this usage, the phrase is usually hyphenated. No, you need to do a hammer-on here—that's why it's not sounding quite right.