Someone thought Intel was too clear in their naming of ISA extensions?
One a more serious note, it looks like RISC-V extensions are single letters, except for X (vendor extensions), S (collection of supervisor-mode extensions), and Z (collection of user-mode extensions).
And RISC-V is designed to be highly modular that the "base" instruction set is really tiny, it even lacks integer multiplication and division (provided via M standard extension). For this reason there are a tremendous number of extensions, and most recent extensions are using the Z prefix, where the second letter is often a relevant single-letter extension (e.g. `Zmmul` is a subset of M with only multiplication) or a mnemonic (e.g. `Zk` prefix is dedicated for cryptographic extensions). No wonder why extension names look so crowded.
One a more serious note, it looks like RISC-V extensions are single letters, except for X (vendor extensions), S (collection of supervisor-mode extensions), and Z (collection of user-mode extensions).