In a row or line; arranged sequentially without gaps or interruption.
Middle English 'arew' from Old English 'on rewe,' combining 'on' (in) and 'rewe' (row, line). The meaning has remained consistent from Old English through Middle English, referring to things arranged in linear order.
This word shows how English used to be much more compact with prepositions—'a' often meant 'in a' or 'on a,' which is why 'arow,' 'arew,' and similar words packed multiple meanings into just two syllables. You still see this pattern in words like 'aboard' and 'afoot.'
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