dis-, dys-
Although these prefixes are homonyms, they are not interchangeable.
The etymology of the prefix dis- comes from Latin, with an original meaning of “apart.” It’s root word, dwis, is related to duo and to bis, with a meaning of “two ways.” Today, the prefix dis- means opposite or opposite of.
The etymology of dys- comes from Ancient Greek, with an original meaning of “bad, evil, ill.” Today, the prefix dys- means bad, ill; hard, difficult; or abnormal, imperfect.
Do not hyphenate after the prefix in most cases. For hyphenation rules, see hyphen.