Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
middle [ˈmɪdl] n середи́на; (waist) по́яс#
adj сре́дний#
in the middle of the night посреди́ но́чи
I'm in the middle of reading it я как раз сейча́с э́то чита́ю
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.