So I was wondering whether there is any archaic word that means "finally" or "at last"?
"At length" is quite archaic, hardly ever used now. At length they fell upon the opposing army. They would also say "at the last" instead of "at last"...
This is from Google's Thesaurus. 'Finally' is identified as having four meanings. Some of the synonyms proposed seem quite ancient to me - 'by and by', 'at length', etc.
finally ˈfʌɪnəli/ adverb adverb: finally 1. after a long time, typically when there has been difficulty or delay. "he finally arrived to join us" synonyms: eventually, ultimately, in the end, by and by, at length, after a long time, after some time; More antonyms: immediately
as the last in a series of related events or items. "a referendum followed by local, legislative and, finally, presidential elections" synonyms: lastly, last, in conclusion, to conclude, in closing, to end, last but not least More antonyms: firstly, initially
used to introduce a final point or reason. "finally, it is common knowledge that travel broadens the horizons" in such a way as to put an end to doubt and dispute. "the need to dispel finally the belief that auditors were clients of the company" synonyms: conclusively, irrevocably, decisively, definitively, definitely, absolutely,
for ever, for good, for all time, once and for all, permanently More antonyms: temporarily
Fynaly - Late 14th Century.. The meaning is the same, but the spelling is archaic.