Phrase: Time immemorial: ancient beyond memory or record.
This phrase came to English in around 1600 CE, it came from the French word ‘immémorial’ which reached English during the Anglo-French period (around 1214 CE) and stayed after the French had stopped governing – this was common with many legal terms. At the time ‘Time immemorial’ was used to establish claims to titles and family lineages; it distinguished between that which was knowable because it was remembered or written down and that which is assumed true because it was too long ago to know. In 1832 the legal meaning of the phrase was updated to ‘Time whereof the memory of man runneth not to the contrary’
‘immémorial’ was derived from the Latin word ‘immemorialis’; the ‘im-’ part here was to later become ‘in-’, which is in this instance didn’t mean ‘against’ as in ‘inverse’ but actually ‘in’ as in ‘input’ or… well ‘in’. The ‘memorialis’ part was Latin for ‘belonging to memory’. So the prahse means literally ‘in memorable time’.