Consuegro is a word we don’t even have an equivalent for in English. A person’s consuegro would be the father-in-law to that person’s son or daughter.

For example: if my son José were married to Maria, then Maria’s parents would be my consuegros. Two mother-in-laws would be consuegras with one another.

I think those are the hardest words to learn, those which have no English equivalent.