delta, delt-; Δ, δ

(Greek: triangular; fourth letter; Δ, δ, of the Greek alphabet)

delt (s) (noun), delts (pl)
A slang term for the deltoid muscle which is often used in the plural: Hank's delts are aching from the excessive exercise he did today.
delta (s) (noun), deltas (pl)
1. The fourth letter of the Greek alphabet (Δ, δ) corresponding to English d, and as a number, it indicates 4.
2. An object shaped like a triangle.
3. Usually a triangular alluvial or sedimental deposit of sand and earth at the mouth of a river.
4. A similar deposit at the mouth of a tidal inlet, caused by tidal currents.

A Greek letter sits at the mouth of many rivers. Noticing the resemblance between the island formed by sediment at the mouth of a river; such as, the Nile and the triangular shape of their letter delta, the Greeks gave the name "delta" to such an island.

The English language incorporated this sense from Greek, although the word delta appeared first in English as the name of the letter, in a work written possibly around 1200 A.D.

The sense of "alluvial deposit" was not recorded until 1555 A.D., when delta was used with reference to the "Nile River delta".

Delta Aquarids (noun) (plural used as singular)
A diffuse meteor shower that appears to come from an area near the star Delta in Aquarius: The Delta Aquarids is an annual meteor shower that reaches a broad peak of activity usually in late July and early August.
delta bar (s) (noun), delta bars (pl)
A ridge-like accumulation of alluvial material formed by a tributary stream that is building a delta into the channel of the main stream.
delta connection (s) (noun), delta connections (pl)
The mesh connection of three elements in a three-phase system in a triangular arrangement resembling the Greek letter delta, with each element connected between two phase conductors, and no connection to the neutral conductor.
delta flat (s) (noun), delta flats (pl)
A low-lying area that is formed by sediment which is deposited by a stream entering a body of standing water: A delta flat is formed when a stream flows into stationary waters; such as, a pond, lake, reservoir, or calm ocean or sea.

A decrease in the velocity of the flowing is decreased in speed and lowers the stream's capacity, causing its contents to be deposited as a delta flat.

delta front (s) (noun), delta fronts (pl)
A narrow, continuous sheet of sand that marks the zone where deposition in a delta is most active.
delta function (s) (noun), delta functions (pl)
In mathematics, the Greek letter δ (lowercase) or Δ (uppercase); often used to represent a small distance or a small change in the value of a variable or function.
delta iron, delta ferrite (s) (noun); delta irons, delta ferrites (pl)
In metallurgy, the high-temperature variety of body-centered cubic iron.
delta kame, kame delta (s) (noun); delta kames, kame deltas (pl)
A hill of stratified sand and gravel that was deposited by a meltwater stream flowing into a proglacial lake.
delta lake (s) (noun), delta lakes (pl)
A lake that is formed along the edge of or within a delta.
delta matched antenna, Y antenna (s) (noun); delta matched antennas, Y antennas (pl)
In electricity, a single-wire antenna to which the leads of an open-wire transmission line are connected in the shape of a Y.
delta matching transformer (s) (noun), delta matching transformers (pl)
A device which matches the impedance to an open-wire transmission line to an antenna: The delta-matching transformer is commonly used for connecting a half-wave antenna to a balanced transmission line.
delta plain (s) (noun), delta plains (pl)
A plain formed by the deposition of alluvium on the landward part of a large delta.
delta ray (s) (noun); delta rays (pl)
An electron emitted when an ionizing element; such as, an alpha particle, passes through matter.

You can see all of the letters of the Greek Alphabet on this page.