The word 'tidy' emerged in Middle English from the earlier word 'tide', meaning 'time' or 'season'. The connection lies in the idea of being 'in good time' or 'timely', which evolved to imply being 'ready' or 'proper'. From this sense of appropriateness and readiness, the meaning further specialized to describe something that is neat, orderly, and well-kept. The informal sense of a 'considerable' sum of money developed in the 19th century, suggesting an amount that is 'handsome' or 'adequate for the occasion'.

The word 'tidy' is a simplex word of Germanic origin. It is not productively formed from separable morphemes in modern English.