In John Webster's play, The Duchess of Malfi, Antonio says of the Duke:
He never pays debts unless they be shrewd turns,
And those he will confess that he doth owe.
I really don't understand what he means. Can someone explain?
I haven't found a reliable source to corroborate, but this set of annotations has a likely interpretation:
This usage comes from a sense of shrewd that was already obsolete in 1828:
Another usage, from Freemasons' proceedings:
And another in a passage about turning the other cheek:
Thus, a shrewd turn is a painful or vexatious deed: injury or insult.