'pro-communistically' originates from the Latin-derived prefix 'pro-' (via Old French/Latin usage) meaning 'for' and from 'communistic', ultimately from French 'communisme' and Latin 'communis' meaning 'common'.

'pro-communistically' developed from the adjective 'pro-communistic' ('pro-' + 'communistic'); 'communistic' traces to 'communism' (French 'communisme'), which itself comes from Latin 'communis'. The adverbial form was formed by adding the adverbial suffix (‑ly) to the adjective.

Initially formed to indicate a stance 'for common ownership' (root idea from 'communis' = 'common'), it evolved to the adverbial sense 'in a manner supportive of communism' used to describe attitudes or actions.