A kettle — a metal (or metal-like) pot for boiling water. Often written in kana; kanji 薬缶 exists.
やかんでお湯を沸かしてから、紅茶を淹れた。
I boiled water in the kettle and then made tea.
古いやかんだが、まだまだ使える。
It's an old kettle, but it's still usable.
Colloquial slang for a bald head (someone who is bald).
笑い話で彼のことを『やかん』と呼んだが、失礼だったかもしれない。
As a joke I called him 'yakan' (bald), but that might have been rude.