'antenoon' originates from Middle English, specifically the phrase 'after noon' (Middle English forms such as 'after none' or 'after non(e)'), where 'after' meant 'after' and 'noon' meant 'midday'.

'antenoon' developed as a regional/dialectal contraction and respelling of Middle English 'after none' (and related spoken forms like 'ant'nōn'), eventually appearing in dialect spellings such as 'antenoon' in Scots and some English regional speech.

Initially, it meant 'after midday' (the time following noon); over time the meaning has remained the same, but the form has become marked as dialectal or archaic compared with the standard 'afternoon'.