zed n.

"mark placed under the letter -c- in certain situations," 1590s, from Spanish cedilla, zedilla, literally "little z," from a Latin-like diminutive of Greek zēta "the letter 'z'" (see zed). The mark, mainly used in French and Portuguese (formerly also used in Spanish), was derived from that letter and indicates a "soft" sound in letters in positions where normally they have a "hard" sound. Sometimes the word is used as though it means the entire character ç.

old name for "Z," 1738, a variant of zed. The guess that it representes S-hard wants evidence.