Heard spelling

jinoecium

Spelled gynoecium. a soft g

Why do people start it with a j?

Because that is what they hear. The soft g of gynoecium is the same consonant as the g of gesture, and English writes that consonant with both g and j.

Nothing in the sound tells you which one to pick. Only the Greek does: gyne began with gamma, and gamma is g.

Say

guy-NEE-see-um, and jy-NEE-see-um is heard just as often

Letters

G-Y-N-O-E-C-I-U-M