Synonyms for Surd (same or very similar meaning)
WordNet sense 1 (a consonant produced without sound from the vocal cords):
voiceless consonantWordNet sense 2 (spoken in soft hushed tones without vibrations of the vocal cords):
whisperedWordNet sense 3 (produced without vibration of the vocal cords):
hard, unvoiced, voicelessFrom the ODE community, based on WordNetadd/edit