'undomed' originates from Old English prefix 'un-' (negative) combined with the noun 'dome', ultimately from Latin 'domus' via Italian 'duomo', where 'domus' meant 'house' and 'duomo' came to mean a cathedral or domed church.

'dome' changed from Latin 'domus' to Italian 'duomo' (meaning a principal church) and via Middle English became 'dome' meaning a rounded roof; the negative prefix 'un-' (Old English) was later combined with 'domed' to form the adjective 'undomed'.

Initially 'domus' meant 'house' in Latin, which shifted in Italian to 'duomo' (a principal church) and then to English 'dome' meaning a rounded roof; 'undomed' thus developed to mean 'lacking that rounded roof'.