Wiktionary
turnip head
n. (context mildly pejorative English) a foolish person.
Usage examples of "turnip head".
They dont take fright at a turnip head and sticks its only when a scarecrows dressed and looks like a man that they keep away.
Cadfael recognised the russet broadcloth, the sturdy build, the round, turnip head with its thinning crown and bushy brown hedge of hair all round the shiny island of bone.
But the great turnip head, the drawn-back mouth full of white teeth almost splitting it in half, was still alive.