"whooping cough," 1670s (Sydenham), from Modern Latin pertussis, from per- "thoroughly," or here perhaps with intensive force (see per), + tussis "cough," a word of unknown origin.
Entries linking to pertussis
per prep.
"through, by means of," 1580s (earlier in various Latin and French phrases, in the latter often par), from Latin per "through, during, by means of, on account of, as in," from PIE root *per- (1) "forward," hence "through, in front of, before, first, chief, toward, near, around, against."