In the description of the menorah in Shemot 25:31, we see mention of the word kaftor כפתור. The word is translated in various translations as knop (an ornamental knob), calyx, sphere, or bulb. In Amos 9:1 and Tzefania 2:14, it refers to the capital of a column. However, none of those fit the meaning in modern Hebrew - "button". Where did that sense originate?
Avineri, in Yad Halashon (page 341), says that while in biblical Hebrew kaftor meant a kind of ornament, the sense of button came from influence from German and French. In those languages, knopf and bouton (respectively) meant both "knob" and "button", and this usage in Hebrew began to feel so natural that it almost seems hard to believe that it was an innovation.
Where does the word originate? Klein and Cassuto both say it's an expansion of the word keter כתר - "crown". Cassuto says that keter "denotes in general anything round", and Klein, who gives the meaning "capital (of a pillar)" before "knob", seems to indicate that the keter was the crown of the column. Stahl quotes a different theory that kaftor is an expansion of the root כפת - "to bind, tie", and Gesenius says it appears to him to be a compound of the roots כפר - "to cover" and כתר - "to crown".
The reason so many theories are presented is the fact that kaftor has a four letter root, which is atypical to biblical Hebrew, certainly a word found all the way back in the Torah. Often times in these cases, we look for a word borrowed from a foreign source. In this case, Sarna in his commentary on Exodus has an curious suggestion:
Hebrew kaftor appears as an architectural term in Amos 9:1 and Zephaniah 2:14, where it designates the capital of a column. Since such were ornamented with a florid design, kaftor most likely refers to the calyx motif. Elsewhere in the Bible, Caphtor denotes the isle of Crete, where this type of ornamentation may have originated. Interestingly, Menahot 28b compares the shape of the kaftor to "Cretan apples."In his commentary on Genesis (10:14), discussing the Capthorim, Sarna writes:
This corresponds to kaptaru in Akkadian texts, kptr in Ugaritic, and probably also to keftiu in Egyptian, all generally identified with the isle of Crete and its environs in the eastern Mediterranean.
So if this the word kaftor (knob) was borrowed from the place Kaftor - then it could easily have arrived from any of those ancient languages.
Kaddari also quotes the gemara in Menachot: כפתורים למה הם דומין? כמין תפוחי הכרתיים, and points to a 1928 article in Leshonenu by the botanist Ephraim Hareuveni (the father of Noga Hareuveni, the founder of Neot Kedumim) that identifies these "Cretan apples" with the gallnuts of a species of the genus Salvia (Hebrew marvah מרווה) native to Crete (likely Salvia fruticosa or Salvia pommifera - for the difference, see here). In fact, in the booklet put out by Neut Kedumim, (for the article in English, see here) on the cover we see a species of salvia which looks very much like the menorah:
Hareuveni concludes that "We frequently find among early civilizations that countries were named for one typical plant growing there ... and so it might have been with the island Kaftor." That's certainly one more possibility...