'athalamous' originates from Greek, specifically from the privative prefix 'a-' and the noun 'thalamos', where 'a-' meant 'not' or 'without' and 'thalamos' meant 'chamber' or 'inner room'.

'athalamous' was formed in scientific/Neo-Latin usage from Greek components 'a-' + 'thalamos' and entered English in technical biological contexts (anatomy, botany) retaining the literal sense 'without a chamber' and later specialized to the senses used in anatomy and botany.

Initially, it meant 'without a chamber' in a general literal sense; over time it evolved into specialized technical meanings such as 'lacking the thalamus (brain structure)' in anatomy and 'lacking a receptacle (thalamus) in botany'.