Where does “Janey” come from?

Janey is an English diminutive formation derived from Jane, which comes from Middle French -ie and Latin -ia suffixes ultimately tracing to Proto-Indo-European -kos.

Ancestry of “Janey”, step by step

Step	Language	Word	Meaning
1	English	jan	Obsolete form of jinn
2	English	Janet	—
3	English	Jane	A woman, often specifically a girlfriend;...
4	French	Jeanne	Jane, feminine of John
5	Old French	Jehane	—
6	Medieval Latin	Johanna	—
7	Latin	Joanna	—
8	Ancient Greek	Ἰωάννα	—
9	Hebrew	יוֹחָנָה	—
10	Hebrew	יוֹחָנָן	God is gracious
11	Hebrew	יְהוֹחָנָן	God is gracious

Every word from Hebrew יְהוֹחָנָן →

Janey — Etymology, Origin & Word History | Etymology Explorer