'baldly' originates from English, formed from the adjective 'bald' plus the adverbial suffix '-ly'. The adjective 'bald' comes from Old English 'bald', ultimately related to Proto-Germanic '*baldaz' (meaning 'bold').

'bald' existed in Old English as 'bald' (with senses related to 'bold' or 'shining' in early Germanic languages); through Middle English it developed the specific sense 'having little or no hair', and in Modern English the adverb 'baldly' arose by adding '-ly' to the adjective.

Initially related to 'bold' (bravery, strikingness), the adjective shifted over time toward the physical sense 'without hair', and the derived adverb developed the figurative sense 'plainly' or 'bluntly' used today.