Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
pen [pɛn] n ру́чка#; (felt-tip) флома́стер; (enclosure) заго́н; (US) (inf)(prison) тюрьма́#
to put pen to paper бра́ться*(взя́ться*perf) за перо́
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.