Bis stands for "second" althought it is not a Russian word. The word have been adopted from French, but it originates from Latin meaning "twice", "second", "encore", "repetition". "Improved" captures the intent of the meaning, which is that the MiG-21bis is an improved model of the original production run. There is also ter which stands for "third", e.g. Polikarpov's I-153 was alternativly called I-15ter and I-152 was I-15bis. Both were further modifications of I-15.

The usage of bis was popular in the prewar perioud and was completely dropped by 60's. Today it is more common to give a whole new designation, e.g. Su-27 and Su-30, although in 1930's Su-30 could most certainly be a Su-27bis, just as improved I-16 became I-16bis. It is also common to use M or U suffixes which mean "improved" and stands for "modernizirovanyi", "usovershenstvonannyi" and "uluchenyi", e.g. Yak-9U, MiG-21PM, Su-30MK. Note that U is most cases stands for "uchebnyi" and is broadly used for the designation of the trainers or two-seaters, e.g. MiG-29UB, Su-25UBG. Use fo bis is not limited to aircraft and it is not a purely aviation term. Bis use to be used for street numbering, e.g. 159bis Lenin Drive is analogous to american 159 1/2. Recall what you yell when you applouse at the opera (that is if you enjoyed it): "Bravo! Bis!". This literally means that you would like to hear the performance once again.

Finally, since it is a word and not an abreviation, it is MiG-21bis rather than all-capital MiG-21BIS. Compare it to MiG-21FM (Forsirovannyi, modifitsirovannyi).

Allen Thomson (thomsona@netcom.com), Margelyn Carpenter (mpcarpe@erols.com), Eric Gross (egross@mailer.fsu.edu)