(as) sharp as a tack

very intelligent.

He may be old in years, but he's still as sharp as a tack and knows what he's talking about.

• dispense with
• dispense with something
• dispose of
• dispose of something
• dissolve into
• dissolve into something
• dive into
• dive into something
• divide-and-conquer
• divide and conquer
• divide and rule
• divide-and-rule
• do a double take
• do a favor
• do a favour
• do a job on
• do a job on someone
• do a job on something
• do a land-office business
• do all the running
• do a mischief
• do a moonlight flit
• do a number on
• do a number on someone
• do a number on something