delta

noun
del·​ta | \ ˈdel-tə How to pronounce delta (audio) \

Definition of delta

 (Entry 1 of 4)

1 : the 4th letter of the Greek alphabet — see Alphabet Table
2 : something shaped like a capital Greek delta especially, geology : the alluvial deposit at the mouth of a river the Mississippi Delta
3 mathematics : an increment of a variable symbol Δ