'ashimmer' originates from the Old English-derived prefix 'a-' (meaning 'on, in, or in a state of') combined with the verb 'shimmer' (Middle English 'schimer'/'shimer'), where 'shimmer' meant 'to shine faintly or tremulously'.

'ashimmer' developed as a compound of 'a-' + 'shimmer' in Early Modern English (seen in poetic/literary usage), evolving from forms like 'a-schimer' or 'ashimer' into the modern single-word form 'ashimmer'.

Initially it meant 'in a state of faint or wavering shine,' and over time it has retained that basic sense, now used chiefly as a poetic or literary adjective meaning 'shimmering'.