↑ kolek in Jiří Rejzek, Český etymologický slovník, electronic version, Leda, 2007
↑ "kolek" in Václav Machek, Etymologický slovník jazyka českého, second edition, Academia, 1968
Etymology
Diminutive of kůl (“stake”), kůl +-ek. Originally referred also to small wooden cylinders used as seal matrixes,[1] and, from that, to the seal impression. The modern meaning derives from that, as seals proving a paid fee were replaced by special paper labels.[2]