\tenrm
LaTeX 2.09 defined a large set of commands for access to the fonts
that it had built in to itself. For example, various flavours of
cmr could be found as \fivrm, \sixrm, \sevrm,
\egtrm, \ninrm, \tenrm, \elvrm, \twlrm,
\frtnrm, \svtnrm, \twtyrm and \twfvrm.
These commands were never documented, but certain packages
nevertheless used them to achieve effects they needed.
Since the commands weren't public, they weren't included in LaTeX2e; to use the unconverted LaTeX 2.09 packages under LaTeX2e, you need also to include the package rawfonts.sty (which is part of the LaTeX2e distribution).