Radioclare wrote:The main words I looked up today were "лазутчик" (spy, but not sure what the difference is between this and "шпион", which is the word I've learned for spy before) and "ефрейторша" (seems to be a military rank).
Лазутчик is a somewhat archaic word, and at its most literal it refers specifically to a spy who sneaks in behind enemy lines in an active war situation. Nowadays шпион and разведчик are somewhat more common.
As a military rank with an added feminitive suffix, ефрейторша could mean two different things depending on the context. Historically the addition of the suffix -ша to a military or civilian rank denoted not a female bearer of the rank in question, but the wife of a man holding that rank. This usage still shows up sometimes, but usually informally or jocularly. Now in formal modern usage military ranks don't have feminine forms even when applied to actual female holders of the rank, so any forms with feminitive suffixes are either as of yet non-standard proposals or informal/slang terms (and the suffix -ша in particular is considered to have pejorative connotations, so it's generally avoided by advocates of introducing more feminine forms into formal usage).