I. ˈdel-tə noun
Etymology: Middle English deltha, from Greek delta, of Semitic origin; akin to Hebrew dāleth daleth
Date: 13th century
1. : the 4th letter of the Greek alphabet — see alphabet table
2. : something shaped like a capital Greek delta ; especially : the alluvial deposit at the mouth of a river
3. : an increment of a variable — symbol Δ
4. : delta wave
• del·ta·ic del-ˈtā-ik adjective
II. adjective
Date: circa 1929
: fourth in position in the structure of an organic molecule from a particular group or atom — symbol δ