I'm voting for "tips". I think that I'm learning that "zap" might be a specific type of nostr post. On nostr, Twitter or anywhere else you can send/receive lightning transactions. Using the same word would be nice, as you mentioned. BUT there is also the nostr NIP-57 which defines how zaps should work.. and not all clients support "zaps" yet. It seems like it's own thing: https://github.com/nostr-protocol/nips/blob/master/57.md