'undeservedly' originates from English, specifically formed from the adjective 'undeserved' and the adverbial suffix '-ly', where '-ly' meant 'in the manner of'.

'undeserved' developed from the negative prefix 'un-' + 'deserved'. 'Deserved' comes from Old French 'deservir' and ultimately from Latin 'deservire' (from 'de-' + 'servire', where 'servire' meant 'to serve'), and the adverb was produced by adding the suffix '-ly' to the adjective.

Initially, the components conveyed 'not served/earned', but over time the combined form came to mean 'in a way that is not deserved' (i.e., without merit or just cause).