Definition of "overthink"

overthink¹

verb
third-person singular simple present overthinks, present participle overthinking, simple past and past participle overthought
1. (archaic) To think about; think over
  Quotations
  But when I dred that wou'd not work, I overthought me of a Wile How I might at my leisure lurk, My graceless Guardain to beguile.
  1695, J.D. Albany, The Banishment of poverty

overthink²

verb
third-person singular simple present overthinks, present participle overthinking, simple past and past participle overthought
1. To think or analyze too much.
2. (rare) To think too highly (of); overestimate
  Quotations
  So to think of self as not to overthink — to think of yourself with sober, moral judgment.
  1859, Henry Ward Beecher, Sermons, page 25