The Etymology of Clear
Clear has migrated through the senses. Its Latin source clarus is built on a Proto-Indo-European root *kelh1- meaning to call or shout (the ancestor of English call and Latin clamare to cry out). Originally a clear voice was a ringing one. By classical Latin clarus had drifted from sound to sight (a clear sky, clear water) and from sight to abstract distinction (a clear argument, a clear man — i.e. famous, illustrious, the source of English clarify, declare, and the name Clara). Old French cler carried all these senses; Middle English took them on around 1290 and added more: clear of debt (1620s), clear meaning empty or unobstructed (1500s), all clear as a military signal (1849), clear as in pure profit (1620s). Clearance, clarify, declaration, and the German loan klar all share the same ringing ancestor.