'rarely-acknowledged' originates from Modern English, specifically the adverb 'rarely' and the past participle 'acknowledged', formed as a compound to describe something that is infrequently admitted or noticed.

'acknowledge' changed from Middle English 'aknowlechen' (or variants such as 'aknowleden') and traces back to Old English elements like 'oncnawan' (to know), eventually becoming the modern verb 'acknowledge'; 'rarely' comes from adjective 'rare' + adverbial suffix '-ly', both established in Middle to Modern English, and the compound arose in Modern English usage.

Initially, the root 'acknowledge' had senses related to 'know' or 'recognize'; over time it shifted toward 'admit' or 'accept'—so the compound originally referenced things 'seldom known' or 'seldom admitted', now meaning 'seldom recognized or admitted'.