Where does “upward compatibility” come from?

upward compatibility (English) comes from English compatibility, from English compatible, from Middle English compatible, from Anglo-Norman compatible, from Medieval Latin compatibilis, from Late Latin compator, from Latin com-, from Latin con- — whale, sea monster; abyss.

Ancestry of “upward compatibility”, step by step

upward compatibility traces back through two separate lines of ancestry.

via English compatibility

StepLanguageWordMeaning
1EnglishcompatibilityThe state of being compatible; in which two or...
2EnglishcompatibleCapable of easy interaction; Able to get along...
3Middle Englishcompatiblecompatible; reconcilable
4Anglo-Normancompatible
5Medieval Latincompatibilisin "compatible beneficium", a benefice which...
6Late Latincompator
7Latincom-allomorph of con-
8Latincon-Used in compounds to indicate a being or bringing...
9Latincumwith, along with; at; -fold
10Old LatincomAlternative form of cum
11Proto-Italickomwith, along, at
12Proto-Indo-Europeanḱómbeside, near, by, with
13Proto-Indo-EuropeanḱeDeictic particle, here; Post-positional...
14Middle Englishkyt
15Russianкитwhale; genitive plural of ки́та
16Old Church Slavonicкитъwhale
17Ancient Greekκῆτοςwhale, sea monster; abyss

via English upward

StepLanguageWordMeaning
1EnglishupwardIn a direction from lower to higher; toward a...
2Old Englishupweardesupwards
3Old Englishupweardturned upwards
4Old English-weardForming adjectives and nouns from adjectives or...
5Proto-Germanicwardazturned; turned toward; facing; Alternative form...
6Proto-Germanicwerþazworthy, valuable
7Proto-Indo-Europeanwert-to turn, to rotate
8Proto-Indo-Europeanwer-to burn; to cover, heed, notice; squirrel
Every word from Ancient Greek κῆτος