- pen-pal (n.)
[pen-pal 词源字典]
- also pen pal, 1931, from pen (n.1) + pal (n.). gradually replacing earlier pen-friend (1919).[pen-pal etymology, pen-pal origin, 英语词源]
- keypal
- "A person with whom one becomes friendly by exchanging emails; an email penfriend", 1990s: from key1 + pal, by analogy with pen pal.