'atremble' originates from the prefix 'a-' (from Old English/Old French, meaning 'in' or 'on') combined with 'tremble', which comes from Old French 'trembler' ultimately from Latin 'tremulāre' (to tremble).

'atremble' appeared in Middle English as a compound form (a- + tremblen/tremblian) and later appeared in Modern English as 'atremble', retaining the same basic form.

Initially it meant 'in a state of trembling' and over time has kept that core meaning, though its use became archaic or literary.