'pro-socialistic' originates from English, formed by the prefix 'pro-' (from Latin 'pro' meaning 'for') combined with 'socialistic' (derived from 'socialism' plus the suffix '-istic').

'pro-' comes from Latin 'pro' meaning 'for, in favor of.' 'Socialistic' developed from 'socialism' (19th century), itself from French 'socialisme' (from 'social'). The compound 'pro-socialistic' is a modern English formation combining these elements to mean 'for socialism.'

Initially, the elements meant 'for' and 'relating to socialism,' and combined they have the straightforward modern meaning 'supportive of socialism'; there is little semantic shift beyond compounding the two parts.