underthigh

• under-thigh
• under thigh

under +‎ thigh

underthigh (plural underthighs)

1. The back of a person's thigh.
   • 1883, Albert Ellery Berg (ed.), The Universal Self-Instructor, New York: Thomas Kelly, “Out-Door Exercises,” p. 350,

     You may walk so as to use neither calf, under-thigh, nor hip to any appreciable extent; but it is hard work to run in any way so as not to develop all three […]

   • 1956, John Howard Griffin, chapter 21, in Nuni‎, Boston: Houghton Mifflin, page 167:

     “She is female!” he bellows, stepping over my head in a fleeting perspective of underthighs and wobbling genitals.

   • 1987, Reginald Hill, Child’s Play‎, New York: Macmillan, Third Act, Chapter 6, p. 160:

     Dalziel […] raised his left leg to scratch his under thigh.

   • 1991, Angela Huth, Invitation to the Married Life‎, New York: Grove, published 1992, Part 2, p. 249:

     His underthighs itched against the wicker seat of his chair.

2. The back upper portion of a pantleg or trouser leg.
   • 1841, Dennis Ellard, A New and Easy Method of the Art of Cutting‎, London: for the author, page 13:

     […] you will, I hope, never omit taking the hip-measure, which will produce a proportionate under-thigh: you will find at all times the under-sides, from the crutch to the hip, longer than the top sides.