The Spanish hilo (cord; thread; string) comes from the Latin for the same, filum. The words sound very different, until we remember that, words in Latin that began with a f- tended to change to h- in Spanish: hijo/filium, and hoja/foliage, for example. Now the hilo/filum make sense!
Interestingly, however, from that same Latin root filum, we get various English words that also quietly show they are descendants of the word for cord or thread. Including: