'stagnate' originates from Latin, specifically the word 'stagnare' (from 'stagnum'), where the root 'stag-' meant 'pool' or 'standing water'.

'stagnare' (Latin) led to Late Latin forms such as 'stagnatus'; through French influence (Old French/Modern French 'stagner'), the term entered English as 'stagnate' in the 17th century.

Initially it referred specifically to standing water ('to be standing/ponding'); over time it broadened metaphorically to mean 'to stop developing or progressing', which is the common modern sense.