The glyph is not a composition. Its width in East Asian texts is determined by its context. It can be displayed wide or narrow. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+03B6 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with 5 other glyphs.
The Wikipedia has the following information about this codepoint:
Zeta (UK: , US: ; uppercase Ζ, lowercase ζ; Ancient Greek: ζῆτα, Demotic Greek: ζήτα, classical [d͡zɛ̌:ta] or [zdɛ̌:ta]zē̂ta; Greek pronunciation:[ˈzita]zíta) is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived from the Phoenician letter zayin . Letters that arose from zeta include the Roman Z and Cyrillic З.