O.E. gerecenian "to recount, relate," from W.Gmc. *(ga)rekenojanan (cf. O.Fris. rekenia, M.L.G. rekenen, O.H.G. rehhanon, Ger. rechnen, Goth. rahnjan "to count, reckon"), from P.Gmc. *rakinaz "ready, straightforward," from PIE *reg- "to move in a straight line." I reckon, used parenthetically, is now dialectal (Southern U.S.), but dates from c.1600 and formerly was in literary use (Richardson, etc.). Related: Reckoning (c.1300).