Thanks for the informative post! However I think asthir may be a false friend in this case. The a- prefix is used to negate sthir in asthir. Sthir in Indian languages means stable, stationary, motionless etc. Kind of like the a- prefix in English sometimes (social, asocial etc.)

But it is not uncommon for word meanings to change in such a way that they take on a meaning exactly opposite of what they used to mean (see for example the meaning of the word nice: http://www.etymonline.com/index.php?term=nice&allowed_in_fra...). I wonder if there is a name for this phenomenon.