Where does “cryptogramme” come from?

cryptogramme (English) comes from English gramme — gram.

Ancestry of “cryptogramme”, step by step

cryptogramme traces back through two separate lines of ancestry.

via English gramme

StepLanguageWordMeaning
1Englishgrammegram

via English crypto

StepLanguageWordMeaning
1EnglishcryptoA secret supporter or follower; Cryptography;...
Every word from English gramme