Theme, n.
Etymology: [OE. teme, OF. teme, F. thème, L. thema, Gr. Do, and cf. Thesis.]
1. A subject or topic on which a person writes or speaks; a proposition for discussion or argument; a text. My theme is alway one and ever was. Chaucer. And when a soldier was the theme, my name Was not far off. Shak.
2. Discourse on a certain subject. Then ran repentance and rehearsed his theme. Piers Plowman. It was the subject of my theme. Shak.
3. A composition or essay required of a pupil. Locke.
4. (Gram.)
4 more senses
A noun or verb, not modified by inflections; also, that part of a noun or verb which remains unchanged (except by euphonic variations) in declension or conjugation; stem.
5. That by means of which a thing is done; means; instrument. [Obs.] Swift.
6. (Mus.)
The leading subject of a composition or a movement.
Shades of meaning
Fernald has no entry of its own for theme; he lists it under topic.
Where he writes about it:
In speaking or writing the general subject or theme may be termed the topic, tho it is more usual to apply the latter term to the subordinate divisions, points, or heads of discourse; as, to enlarge on this topic would carry me too far from my subject; a pleasant drive will suggest many topics for conversation. — from topic