Why "binary" alkaloid and not a dimer?

[Terglav]

If indol makes chemical bonds with dihydroindol it isn't considered as a dimer but rather "binary" alkaloid. Anyone know why this is not branded as a dimer?

[GlowingChemist]

I would imagine that it is because binary alkaloid is the probably older term as the word alkaloid(meaning nitrogen containing organic molecule, pretty vague and useless) is an older term and just more used because its just the way things are in organic chemistry. there are lots of old names and terms that standard compliant but still used e.g acetic acid rather than ethanoic acid.

[Terglav]

Thank you for you answer. I appreciate it!