That's quite problematic really. The word does certainly not come from the first reich and its Romance roots appear questionable. As etymonline points out, the er-ending should regularly be lost from Anglo-Norman-French. Therefore it seems more likely to me that it is a Nordic influence, as
-er is the usual verb ending e.g. in Swedish,
jag kommer ham (I come home), and it is still used as a verb at the end of your excerpt,
tendered. In addition,
to extend ones wishes shows that both words can be understood to mean "to offer", and
ex-, es-, s- appears particularly often in French as if reanalyzed after a minor sound change (conversely, t > ts, tsh, ch is much more common), and this is probably still seen in German
stunden (to
extend a dead-line) if other explanations (i.e. from
Stunde "hour", or akin to
stun). Before this background it's nigh impossible to guess the origin, if Latin was still prefered and often corrupting native words in writing. In particular, it could be equivalent to "currency" if cognates mean approximately
current, on going, cp. German
ständig, also the verbal phrase
Kosten erstatten. However it's likely more complicated than that, or "immitative" as the OED would say.
So, all things considered, Breckinridge is likely refering to one of those maximally English etymologies.
I reckognize that this has little bearing on an 18th century interpretation if the word was free to be interpeted. It just has nothing to do with literal interpretation, and beyond that I'm not really interested, or not equipped to argue on the basis of case law.