su·pine (spīn′, s-pīn)
1. Lying on the back or having the face upward.
2. Having the palm upward. Used of the hand.
3. Marked by or showing lethargy, passivity, or blameworthy indifference: "No other colony showed such supine, selfish helplessness in allowing her own border citizens to be mercilessly harried" (Theodore Roosevelt).
In Latin grammar, a verbal noun used in only a few syntactic constructions and occurring in only two cases, an accusative in -tum or -sum and an ablative in -tū or -sū. The accusative form of the supine is sometimes considered to be the fourth principal part of the Latin verb.
[Middle English supin, Latin verbal noun, from Late Latin supīnum (verbum), (verb) lying on its back, (verb) going back, neuter of Latin supīnus; see upo in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.