against
UK[əˈɡenst]US[əˈɡenst]
prep
In opposition to or disagreement with someone or something.
prep
In contact with or supported by a surface.
prep
As a protection from or in preparation for something.
Etymology
The word 'against' originated in Middle English as 'ageynes,' a combination of the prefix 'a-' (meaning 'on' or 'to') and 'gegn,' an Old English root meaning 'direct' or 'straight,' which is related to the word 'again.' The core sense was 'in a line facing, opposite to.' Over time, its form contracted and its meaning expanded from the physical sense of being opposite or in front of something to encompass abstract notions of opposition, contact, and preparation. It evolved from a directional term into a versatile preposition expressing contrast, physical adjacency, and defensive purpose.
Analysis
The word is a simplex form derived from a Middle English phrase. It is not productively composed of separable morphemes in modern English.
Examples
He voted against the proposed law.
She leaned the ladder against the wall.
They inoculated the population against the disease.