Upsilon

Upsilon (US: , UK: ; uppercase Υ, lowercase υ; Greek: ύψιλον ýpsilon [ˈipsilon]) or ypsilon is the twentieth letter of the Greek alphabet. In the system of Greek numerals, Υʹ has a value of 400. It is derived from the Phoenician waw (𐤅).

Etymology

The name of the letter was originally just υ (y, also called ὑ hy, hence hyoid, meaning 'shaped like the letter υ'), but the name changed to υ ψιλόν (=υ psilon, 'u-plain' or 'u-simple') to distinguish it from οι, which had come to have the same [y] pronunciation.

Pronunciation

In early Attic Greek (6th century BC), it was pronounced [u] (a close back rounded vowel like the English "long o͞o"). In Classical Greek, it was pronounced [y] (a close front rounded vowel), at least until 1030. In Modern Greek, it is pronounced [i]; in the digraphs ⟨αυ⟩ and ⟨ευ⟩, as /f/ or /v/; and in the digraph ⟨ου⟩ as /u/. In ancient Greek, it occurred in both long and short versions, but Modern Greek does not have a length distinction.

As an initial letter in Classical Greek, it always carried the rough breathing (equivalent to h) as reflected in the many Greek-derived English words, such as those that begin with hyper- and hypo-. This rough breathing was derived from an older pronunciation that used a sibilant instead; this sibilant was not lost in Latin, giving rise to such cognates as super- (for hyper-) and sub- (for hypo-).