My DNS server is SOA for …
This is the Frequently Given Answer to such statements.
"SOA" stands for "Start of Authority", and that is not a term that applies to DNS servers. A DNS server cannot be termed a "start of authority". The concept simply has no applicability to DNS servers.
The concept applies, inasmuch as it applies at all, to DNS database
content, with a database resource record of the
SOA type denoting the apex of a "zone of authority"
within the DNS data.
The terms that you are groping for are "content DNS server" and "master".