pn-

consonant sound in some English words derived from Greek. The p- typically is silent in English but pronounced in French, German, Spanish, etc.

It is to be desired that it were sounded in English, also, at least in scientific and learned words; since the reduction of pneo- to neo-, pneu- to new-, and pnyx to nix, is a loss to etymology and intelligibility, and a weakening of the resources of the language. [OED]