Yes, and also anepsios for nephew. However, the usage is that adelphos is a generic term of relatives of roughly the same age, when the specific narrow term cannot be applied to everyone in the group, or for some other reason not advisable. We see that expansive usage throughout the scripture and it is still common in the Middle East and Greece today.
One simple reason to use the generic term is that Jesus liked to use the word "brother" to refer to His disciples. Imagine the gospel where strangers are called warmly "brothers" whereas the flesh and blood relatives coolly "cousins". It would have been outright confusing.
"We see that expansive usage throughout the scripture and it is still common in the Middle East and Greece today."
Indeed it is. My cousins and I often refer to each other as brother or sister. And cousins in the generation before us as aunt or uncle and there is absolutely no distinction of degrees of kinship, like 3rd or 2nd cousins. The overall unit really is first "family" which can be a huge group and then "patriotis", a word I can't really translate but maybe Alex can. It is like calling someone a family member but it really refers more to someone from one's family's region and it is very like a term of kinship. Anglo Saxon or Western European notions of kinship just don't apply east of the Adriatic and so far as I know, they never did.