When used as a simple adjective in English, singular usually means unique.
The singular is one of two grammatical numbers in English; the other is the plural.
In mathematics singular has a number of meanings
SINGULAR is also the name of a computer algebra system.
See also gravitational singularity.
Singular (أَحَدٌ) is one of God's Names as described in Sura 112 in the Quran:
"Say: He is Allah, Singular. Allah, the Absolute. He begetteth not nor was begotten. And to Him have never been one equal."