The word "reckon" generally means to think, believe, or consider something. It can also refer to estimating or calculating a value or amount. For example, when you reckon something, you're making a judgment or an opinion about it.
The word "reckon" comes from the Old English "recenan," meaning "to account for or to calculate." It has roots in the Proto-Germanic "*rekanō" and is related to the Old Norse "reikna," which also means to count or calculate.