'on-and-off' is formed from the simple words 'on', 'and', and 'off'. 'on' originates from Old English 'on' (from Proto-Germanic '*an') meaning 'in, on'; 'off' originates from Old English 'of'/'off' (from Proto-Germanic '*af') meaning 'away'; 'and' originates from Old English 'and' meaning 'and'.

'on' and 'off' have been used in Old and Middle English as basic adpositions/adverbs; the combined phrase 'on and off' (also written 'on-and-off' or 'off and on') appears in Early Modern English to describe alternating states and has continued into modern usage.

Initially the words described opposite states or directions ('on' vs. 'off'); over time the combined phrase came to be used idiomatically to mean 'alternately' or 'intermittently', the meaning it retains today.