The "ps" spelling in English comes from the Greek letter "psi" (ψ), representing the "ps" sound. 
When Greek words were adopted into Latin and then into English, the "ps" spelling was kept to preserve the original pronunciation.

Inglish simplifies "ps" to "s"

Examples:
    psychology: From Greek "ψυχολογία" (psychologia), meaning "study of the mind."
    psalm: From Greek "ψαλμός" (psalmos), meaning "song" or "hymn."
    pseudonym: From Greek "ψευδώνυμον" (pseudonymon), meaning "false name."

Inglish:
    sykólogy
    salm
    súdonim