You missed flex from lex.

And then:

* getty; agetty ("alternative"); mingetty ("minimal"); mgetty (I always think "modem" myself); uugetty ("UUCP"); fgetty ("fast"); and ngetty (probably "Nikola")

- https://unix.stackexchange.com/a/316279/5132

* ex; vi; stevie; elvis; calvin; elwin; javi; lemmy; pvic; trived; vigor; vile; vip; virus; winvi; xvi; vim, view, evim, exim, eview, rvim, rview, gvim, gex, gview, rgvim, rgview, vimdiff, and gvimdiff (VIM); nvi; and nvim (NeoVIM)

- http://www.guckes.net/vi/clones.php3

* pax, a peace treaty in the tar versus cpio argument

In math and physics there is the Pin group which is named because it relates to the Spin group (named after spin like of an electron) in the same way that SO (special orthogonal group) relates to O (orthogonal group) and SL (special linear group) relates to GL (general linear group). This is something some mathematicians find quite amusing.

Edit: also some say rng which is a ring without an identity (without an i). I think there are others similar to this.

elm stands for ELectronic Mail, if I'm not mistaken.