CzechPřibýtTo be an addition (to a group, and thereby make said group grow in volume).

(This is a completely normal word, nothing quirky about it. I just find it kinda weird that there isn't a direct English translation for it.) Link: Example sentence: "Do mé sbírky *přibyli* dva motýli." Translation: "Two butterflies *have been added* to my collection." or perhaps: "Two butterflies *have newly appeared* in my collection." There's also the opposite "ubýt" for when the number of members of a group decreases.