МЦСТ (MCST) was an abbreviation for "Московский центр SPARC-технологий", now it's just a meaningless letters. ARM in computer name means probably "Автоматизированное рабочее место" - "Automated workstation"

Oddly enough the name is apparently due to Dave Ditzel, who was financing MCST at the beginning. The same Ditzel that went on to found Transmeta 3 years later.

PS. I didn't know that actually, just followed few links from the Elbrus Wikipedia page and bumped into an interview with the MCST founder from 2003 [1] - he basically says there that in the early 90s there was a spike of interest in the tech behind Elbrus 3. First it was HP, then it was Ditzel, who was at that time with Sun. Ditzel eventually quit Sun and went on to found Transmeta and develop the Crusoe. Babayan then goes on to say that "We are effectively on a market, except we are not seeing any money. But on the other hand without Ditzel we would've not gotten any (research) money and all our work would've died." Interesting stuff.

[1] http://offline.homepc.ru/2003/81/24693/