Earlier on in the northern lands, including Anglo-Saxon regions, they were known as 'breeks' (also 'breeches').
A famed Danish Viking king named Ragnar 'Lothbrok' would have been known in modern English as 'Leather breeks', the nickname becoming the name 'Ladbroke', a well known chain of 'bookies' or 'turf accountants' (betting shops).
Although it's only one item, we've got two legs. Most people in the north of England of working class descent call them breeches.
In a play on words: 'I've burnt my breeches' (the original is '... burnt my bridges), i.e., can't go back. Back in the 60's and 70's we called them 'strides', remember? That seems to have gone the way of all things.
In Scotland they're called 'trews' or 'troosers' (as in Andy Stewart's song, 'Donald, weere's yer troosers?'), worn by the military in winter by some regiments instead of the kilt.