'asmolder' originates from the prefix 'a-' (from Old English on/ān, meaning 'in' or 'on') combined with 'smolder' (Old English/Middle English), where 'smolder' meant 'to burn slowly.'

'asmolder' developed as a prefixed form of Middle English 'smolden/smolderen' (or similar variants) and was used in early modern English as 'a-smolder' or 'asmolder' to mean 'in a state of smoldering.'

Initially it simply indicated being 'in the condition of slow burning'; over time it remained close to this sense but became less common and more literary/archaic compared with the unprefixed 'smolder.'