This is adapted from a fill described in the article "5-by-5 Palindromic Word Squares" from Word Ways (1976). Worth a read!
The original square used STRAD (nice nickname for a fancy violin) and TRAPA (obscure name for genus of Eurasian aquatic perennial herbs: water chestnut). I went with STREP (as in strep throat, though STRAD is a better word) and TRADE (much more approachable than TRAPA).
