under a spell Definition

spell²
noun

1. A set of words which, especially when spoken, is believed to have magical power, often of an evil nature.

Example: a magic spell
2. Any strong attracting influence; a fascination.

Example: found the spell of her personality incredibly powerful

Idiom: cast a spell on someone (cast a spell upon someone)

To direct the words of a spell (towards them), especially in the hope that something bad will happen.

Idiom: under a spell

Held by the influence of a spell that has been cast.

Idiom: under one's spell

Captivated by their influence.

Etymology: Anglo-Saxon, meaning ‘narrative', from spellian to speak or announce.