\tenrm
LaTeX 2.09 defined a large set of commands for access to the fonts
that it had built in to itself. For example, cmr might
appear as \fivrm, \sixrm, \sevrm,
\egtrm, \ninrm, \tenrm, \elvrm, \twlrm,
\frtnrm, \svtnrm, \twtyrm and \twfvrm, according
to the size it’s being typeset at.
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 LaTeX 2e; to use the unconverted LaTeX 2.09 packages under LaTeX 2e, you need also to include the rawfonts package (which is part of the LaTeX 2e distribution).
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=oldfontnames