As far as I know, the word “δημάρχης” does not exist in modern Greek. We use the word “δήμαρχος” (= mayor). I don't know if in some areas in Greece the word "δημάρχης" is used idiomatically instead of "δήμαρχος"or with another meaning. I have never heard it.
The word “στελεχάρχης” appears in current Greek in texts that have to do with business administration. It seems to be a neologism (a newly created word) which means “director, chief of other executives”.
Etymology: “στελεχάρχης” is a compound word, which comes from the words “στέλεχος” (= executive) and the ending “-άρχης”. Τhe ending “-άρχης” comes from the ancient Greek verb “άρχω” (= to lead, to be a chief).
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.
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