Greek

 Words in English beginning with ph, rh, ps, and ch (when these letters are pronounced as in chasm) are of Greek origin. Some words beginning with th as well. This etymology becomes invisible in Spanish, with its phonetic spelling, so photophobia becomes fotofobia, chaos is caos. I tell my students, many of them premeds, that they can tell the words in Spanish of Greek origin by thinking of the English cognate of filosofía or seudónimo. For medical professions or just to be an educated person it is useful to have a basic Greek lexicon of prefixes and suffixes like phobia, photo, pseudo, phono, psycho, neuro, algia,  bio, gyno, optho, geria, pedi.