The Collaborative International Dictionary of English v.0.48:
Reckon \Reck"on\, v. i.
1. To make an enumeration or computation; to engage in
numbering or computing. --Shak.
2. To come to an accounting; to make up accounts; to settle;
to examine and strike the balance of debt and credit; to
adjust relations of desert or penalty.
"Parfay," sayst thou, "sometime he reckon shall."
To reckon for, to answer for; to pay the account for. "If
they fail in their bounden duty, they shall reckon for it
one day." --Bp. Sanderson.
To reckon onTo reckon upon, to count or depend on; to
include as a factor within one's considerations.
To reckon with,
(a) to settle accounts or claims with; -- used literally
(b) to include as a factor in one's plans or calculations;
(c) to deal with; to handle; as, I have to reckon with
raising three children as well as doing my job.
[1913 Webster +PJC]
After a long time the lord of those servants
cometh, and reckoneth with them. --Matt. xxv.
To reckon without one's host, to ignore in a calculation or
arrangement the person whose assent is essential; hence,
to reckon erroneously.