pants v. trousers v. knickers

Many of the discrepancies between British and American English occur below the waist.

Garment	US name	UK name
any waist to ankle outer garment	pants	trousers
formal waist to ankle outer garment with belt-loops and a fly-front	trousers
waist to below the knee outer garment	knickers	plus-fours
any hip to groin undergarment	underwear	pants
women’s hip to groin undergarment	panties	knickers

 

H2G2 on pants v. trousers

Wikipedia on trousers

Wikipedia on knickers