'mediocrely' originates from English, specifically from the adjective 'mediocre' plus the adverbial suffix '-ly', where the suffix '-ly' meant 'in the manner of.'

'mediocre' entered English from French 'médiocre', which in turn comes from Latin 'mediocris' (meaning 'moderate' or 'ordinary'); the English adverb 'mediocrely' was formed by adding '-ly' to 'mediocre'.

Initially the root 'mediocris' in Latin meant 'of middle value' or 'moderate'; over time in English it came to mean 'of only moderate or low quality', a sense preserved in 'mediocre' and 'mediocrely'.