He/she means the Soviet astronomers called themselves cosmonomers. Like astronauts and cosmonauts, har har.
> He/she
Use "they" when you do not know the subjects gender/sex/whatever. Much cleaner to look at and read.
I considered "they" but worried that it could be parsed as coreferential with matrix12's "they," so I used he/she which, because it is singular, refers unambiguously to the previous speaker, matrix12 himself/herself.
I don't think that's an actual word. Perhaps a mistranslation?