sonder

to probe (test with a probe); to probe (test the depth of something); to probe (look carefully around); to probe (ask someone many questions, in order to find something out); to survey and take measurements using a weather balloon

Inherited from Middle French sonder, from Old French sonder (“to plumb”), from sonde (“sounding line”), from Old English sund- (“sounding”), as in sundġierd (“sounding-rod”), sundlīne (“sounding-line, lead”), sundrāp (“sounding-rope, lead”), from Old English sund (“ocean, sea”), from Proto-West Germanic *sund, from Proto-Germanic *sundą (“a swim, body of water, sound”), from Proto-Indo-European *swem(bʰ)- (“to be unsteady, swim”). Cognate with Old Norse sund (“swimming; strait, sound”). More at