I just don’t see any difference
ar·rest (-rst)
v. ar·rest·ed, ar·rest·ing, ar·rests
v.tr.
1. To stop; check: a brake that automatically arrests motion; arrested the growth of the tumor.
2. To seize and hold under the authority of law.
3. To capture and hold briefly (the attention, for example); engage.
v.intr.
To undergo cardiac arrest: The patient arrested en route to the hospital.
n.
1.
a. The act of detaining in legal custody: the arrest of a criminal suspect.
b. The state of being so detained: a criminal under arrest.
2. A device for stopping motion, especially of a moving part.
3. The act of stopping or the condition of being stopped.
From a legal perspective there is a big defference. For example, if you’ve ever been pulled over for a traffic stop, you’ve been detained. It is only for the purpose of conducting an investigation and is generally accepted to be limited in time. If during that traffic stop the police determine that you are intoxicated, then you will be arrested and taken into custody where you will be processed for the purpose of further legal proceedings.
When someone is under arrest, they are told, “You are under arrest for...”. Except when a traffice citation is being issued. In that case, It is an “arrest” and the subject is signing the citation, which is a promise to appear. He is being released on his recohnizance.
A detention for investigation is just that, they are temporarily detained.
Quoting a funk and wagnalls is not the same as researching a Deerings. I think that is what gets most people confused.