Psalm begins with ps-, one of the Greek clusters English inherited on paper and abandoned in speech. The Greek is psalmos, "a song sung to a harp," originally the plucking of the strings, from psallein, "to pluck, twitch, play a stringed instrument."
The spelling had to be fought for. Old English had it as psealm but also as plain sealm and salm, and Old French had both psaume and saume — the p was widely dropped in writing as well as speech. Etymonline puts it exactly: after some hesitation, the pedantic ps- spelling prevailed in English, as it did in German and French. But there is a twist. Those neighbouring languages pronounce the p. English is almost alone in writing the letter and refusing to say it, which makes psalm a small monument to spelling for the eye rather than the ear.
psalm (n.) "sacred poem or song," especially one expressing praise and thanksgiving, Old English psealm (West Saxon sealm ; Anglian salm ), partly from Old French psaume , saume , and partly from Church Latin psalmus , from Greek psalmos "song sung to a harp," originally "performance on stringed instrument; a plucking of the harp" (compare psalt ē s "harper"), from psallein "play on a stringed instrument, pull, twitch" (see feel (v.)). Used in Septuagint for Hebrew mizmor "song," especially the sort sung by David to the harp and collected in the Old Testament Book of Psalms . Related: Psalmodize . After some hesitation, the pedantic ps- spelling prevailed in English, as it has in many neighboring languages (German, French, etc.), but English is almost alone in not pronouncing the p- .
psalm came in through Greek, and its spelling follows that family's conventions.
How that family writes these sounds
| a bare /n/, /t/, /s/, /z/ at the start | put the silent letter back on the front: pn-, pt-, ps-, mn-, x-pneumonia, pterodactyl, psalm, mnemonic, xylophone |
What gives it away on the page
| ps-, pn-, pt-, mn-, x- | Initial clusters English can't actually pronounce, so it silences the first letter.psalm, pneumonia, pterodactyl, mnemonic, xylophone |
Placing it without the spelling
| a medical or technical word starting with a bare /n/, /t/, /s/, or /z/ | Greek — the letter you can't hear comes firstpneumonia, pterodactyl, psalm, xylophone |