'Eastern-themed' originates from Modern English as a compound of 'Eastern' and 'themed'. 'Eastern' is the adjectival form of 'east' (Old English 'ēast' with the suffix '-ern'), and 'themed' comes from 'theme' (from Greek 'thema' via Latin and French), with the -ed suffix forming an adjective.

'east' comes from Old English 'ēast' (from Proto-Germanic *austaz) meaning the direction where the sun rises; the adjectival suffix '-ern' produced 'Eastern' in Middle English. 'Theme' entered English from Greek 'thema' (via Latin and French) meaning 'something set or placed'; in Modern English 'theme' meant a subject or motif, and adding -ed produced 'themed' as an adjective (e.g., 'themed party'), which then combined with directional adjectives to form compounds like 'Eastern-themed'.

Initially, 'east' simply denoted direction ('where the sun rises'), and 'theme' referred to a subject or motif; over time the compound 'Eastern-themed' came to mean specifically 'styled or decorated using Eastern motifs', a semantic combination of location/culture ('Eastern') and motif-based styling ('themed').