"Jag har på mig en tröja under jackan."
Translation:I wear a sweater under the jacket.
I think it’s originally Germanic, as the meaning shift from originally “between” (cf. Latin inter) to “under” happened in German and English too. In German, the original meaning is preserved as a prefix in some words: unterbrechen (“to under-break”, meaning “to interrupt”), Unternehmen (“under-take”, meaning enterprise) – hey, they are direct translations from their Latin/French/English counterparts!