Grandfather clock

Grandfather clocks are more properly called a Longcase clocks. The clocks live up to their name as they are very tall – a feature that is alluded to in Henry Clay Work’s 1876 song Grandfather’s Clock, which is the source of the name:

My grandfather’s clock
Was too large for the shelf,
So it stood ninety years on the floor;
It was taller by half
Than the old man himself,
Though it weighed not a pennyweight more.
It was bought on the morn
Of the day that he was born,
And was always his treasure and pride;
But it stopped short
Never to go again,
When the old man died.

Smaller models of longcase clock are sometimes called grandmother (nominally, shorter than 6′ 3″) and grand-daughter (shorter than 5′ 2″) clocks. These names derive from grandfather clock and have no other connection to grandmothers or grand-daughters.