Where does “Betwixtmas” come from?

Betwixtmas (English) comes from English betwixt, from Middle English bitwixe, from Old English betwēox, from Old English be-, from Old English hrōpan, from Proto-West Germanic hrōpan, from Proto-Germanic hrōpaną, from Proto-Indo-European ḱer- — army.

Ancestry of “Betwixtmas”, step by step

Betwixtmas traces back through two separate lines of ancestry.

via English betwixt

StepLanguageWordMeaning
1EnglishbetwixtBetween, specifically between two objects
2Middle EnglishbitwixeIn the position that separates (two things); in the middle
3Old Englishbetwēoxbetween
4Old Englishbe-a productive prefix usually used to form verbs...
5Old Englishhrōpanto shout, proclaim; cry out, scream, howl; to cry...
6Proto-West Germanichrōpanto cry out, to call, to shout
7Proto-Germanichrōpanąto cry out, call, shout
8Proto-Indo-Europeanḱer-to grow, to make grow, to nourish; to plait,...
9Proto-Indo-Europeankr̥-to turn, to bend
10Proto-Indo-Europeanker-army

via English Christmas

StepLanguageWordMeaning
1EnglishChristmasA festival or holiday commemorating the birth of Jesus Christ and incorporating various Christian, pre-Christian, pagan, and secular customs including gift-giving, which in Western Christianity is celebrated on December 25 (Christmas Day) in most places
2Middle EnglishCristemasseChristmas the 25th of December
3Old EnglishCristes mæsseChristmas
4Old Englishmæssemass
5Vulgar LatinmessaEucharist, dismissal; Eucharist; dismissal;...
6LatinmissaMass; Christian eucharistic liturgy; nominative...
7Latinmissumaccusative supine of mittō; inflection of...
8Latinmittōto send, dispatch, cause to go, let go, release, discharge
9Proto-Italicmeitōto put forth, put out
10Proto-Indo-Europeanmeyth₂-to hurt; to exchange, remove; to replace, to...
Every word from Proto-Indo-European ker-Every word from Proto-Indo-European kr̥-Every word from Proto-Indo-European ḱer-