AKTI has some interesting information about the definitions of "dirk" and "dagger": https://www.akti.org/resources/akti-app ... ns/#dagger
. Generally, if it looks "stabby" and it's double-edged, then it's either a dagger (if the blade is long) or a dirk (if the blade is short and/or worn with your kilt). The reality is, if the arresting officer calls it a "dirk" or "dagger," than that's what you're carrying.
The legality really depends on the state's specific laws (both black-letter and case law) and the context in which the knife is being used. For example, my wife's dive knife in Hawaii was a double-edged titanium dirk with a plain edge on one side and a serrated edge on the other. However, Hawaii knife law specifically said (based on a case from the 1970s) that a dive knife did not
constitute a dirk/dagger if used for diving. Walking around Waikiki or Chinatown at 1 AM with the same knife would have been a different story, though, since the knife would have counted as a dirk in that context.
[General Caveat: I'm not a lawyer, so please do not interpret any of the above information as legal advice. As a pre-law professor, I'm entitled to discuss black-letter law and case law, but not apply those findings to the particular facts of your case. If you want to know about the laws in your particular area, contact a licensed attorney.]