Also, it is hard to say what an opposite is. Is enemy the opposite of friend? Friend might be contrasted with enemy in a proverb like, "A thousand friends are not enough, one enemy is too many." But in naturally occurring language friend is more often connected with words like the following: "family, friends and acquaintances," "friends, neighbors, co-workers," "friends and acquaintances," etc. Hopefully, the new dictionary of collocations will contain series like these.