PIE base ‘To shout, call, cry’.
Other derivatives include declare, claim, conciliate, council, reconcile (calling together again), nomenclature, and calendar, from Latin kalendæ ‘the calends’, the first day of the month, when it was publicly announced on which days the nones and ides of that month would fall.
[Pokorny: *kel-6, k(e)lē-, k(e)lā, pp. 548–550.]