The word "most hissing" suggests a strong and intense sound resembling a snake's hiss. Synonyms for this phrase include "most sibilant," "most serpent-like," "most menacing," "most venomous," and "most sinister." "Most sibilant" describes a sound that is high-pitched and has a prominent 's' sound. "Most serpent-like" amplifies the snakelike quality of the sound, emphasizing its slithering and sneaky nature. "Most menacing" suggests a threatening tone, while "most venomous" underscores the potential danger and poison associated with the sound. Finally, "most sinister" denotes an ominous, foreboding quality that evokes feelings of fear and dread.