/ˈmɒnəʊθiɪzəm/
[noun] The belief that there is only one God. This idea is central to religions such as Christianity, Islam, and Judaism.
The word 'monotheism' is surprisingly young — it was only coined in the 1600s, long after the belief itself had existed for thousands of years.
The story of the word 'monotheism' begins not with ancient priests or prophets, but with a seventeenth-century Scottish philosopher named Henry More. In 1660, More needed a precise, scholarly term to describe the belief in a single God, and so he constructed one from Greek building blocks. It was a word invented to name something that had already existed for millennia — a label arriving long after the idea it described had shaped civilisations, wars, and entire ways of understanding the universe.
The first piece of the word is the Greek prefix 'monos', meaning 'alone' or 'single'. This root appears in dozens of English words: Ancient Greek monos → English 'monk' (a person who lives alone), Ancient Greek monos → Latin monachus → Old French moine → English 'monk'; Ancient Greek monos → English 'monopoly' (control by a single party); and Ancient Greek monos → English 'monastery', 'monologue', and 'monarch'. In every case, the core idea is one-ness, singleness, or isolation from all others.
The second piece is the Greek word 'theos', meaning 'God' or 'a god'. This root is equally prolific in English. Ancient Greek theos → Latin deus → Old French dieu, but the Greek form also travelled directly into scholarly English, giving us 'theology' (the study of God or gods), 'theocracy' (government by divine authority), 'atheism' (Ancient Greek a- meaning 'without' + theos, meaning belief in no god at all), and 'pantheism' (Ancient Greek pan meaning 'all' + theos, the belief that God and the universe are one and the same thing). The suffix '-ism', added to form 'monotheism', comes from Ancient Greek '-ismos', a suffix used to name a system of belief or practice.
More combined these elements — monos + theos + ismos — to produce 'monotheism', and the word passed smoothly into educated English use in the late seventeenth century. It appeared at a time when European scholars were actively comparing the world's religions, and they needed a vocabulary precise enough to draw clear distinctions. 'Monotheism' stood in direct contrast to 'polytheism' (Ancient Greek polys, meaning 'many', + theos — the belief in many gods), and later to 'deism' and 'pantheism'.
What is remarkable about the word is how artificial and deliberate its birth was. Unlike words such as 'God' or 'prayer', which grew organically through centuries of use by ordinary people, 'monotheism' was assembled in a scholar's study like a piece of philosophical furniture. It belongs to a family of invented Greek-derived terms that the seventeenth and eighteenth centuries produced in great numbers, as thinkers tried to categorise human belief systems the way naturalists were categorising plants and animals. The word did not describe a new reality — it simply gave an old reality a new, tidy name.
Today, 'monotheism' is used by scholars, students, and ordinary speakers alike to describe one of the most widespread and influential ideas in human history. It sits quietly in textbooks and conversations, giving no hint that it is, historically speaking, a young word wearing ancient Greek clothes — a modern invention built to house a very ancient thought.