'atrickle' is formed from the prefix 'a-' (from Old English prepositional/adverbial use meaning 'on, in, to') combined with 'trickle' (Modern English).

'trickle' originates from Middle English 'trikelen' (an imitative or frequentative formation referring to small drops or a thin stream). The prefix 'a-' as in many older English adverbial/adjectival forms (compare 'ashore', 'afloat') was attached, producing 'a-trickle' and later written as one word 'atrickle' in some historical texts.

Initially it meant 'in or as a trickle, in small drops'; over time the meaning has remained similar but the form has become archaic or rare in modern usage, largely replaced by phrases like 'in trickles' or the verb 'to trickle'.