yes and no,

and unfortunately I am bridging knowledge from bitcoin here and not aware of the details for nostr keys specifically so take this all with a huge grain of salt.

the (single) nsec is used to derive the (single) npub with secp256k1 cryptography, which is the same as bitcoin priv/pub keys. so it is one-for-one, and only the one npub will exist for the nsec.

in bitcoin, BIP-32 added hierarchical deterministic derivation, which treats the secret key as a master key and generates sub-keys (additional private keys) which are unique and can be used to generate their own public keys.

this is effectively unlimited.

but in nostr, there is no BIP-32 equivalent to my knowledge, meaning we do not have a standard for generating HD derivations.

in theory, you can still generate them yourself.

but in practice, because this is not a standard for the nostr protocol, this would mean you are creating multiple nsec/npub pairs and would have to figure out how to generate them in a compatible format to what your client is accepting for valid keys.

otherwise to integrate your “new keys” (which all come from and are usable with your “master” private key) in a seamless way you would have to create your own client and introduce a bunch of non-standard stuff..

i believe this is how it works but again could be completely wrong.

basically we need a NIP-32 equivalent and then HD derivations could allow all this “by default” for nostr clients