Onstrike The storage compartment of a car began as a box strapped to the back - in French a box is a "boite", (said as bwat) which became "boot". You could also strap on your trunk. The UK says boot, the USA says trunk.
Freedomfromthepast "In Scotland and Ireland, young people took part in a tradition called guising, dressing up in costume and accepting offerings from various households. Rather than pledging to pray for the dead, they would sing a song, recite a poem, tell a joke or perform another sort of “trick” before collecting their treat, which typically consisted of fruit, nuts or coins." They still do. They don't dress up a stuffed effigy of Guy Fawkes and ask for a penny for the guy, they dress themselves up and sing, recite or tell jokes for their payment of (these days) sweets. No tricks.
“fell pregnant” We also say "fell ill" They both imply that the fall was sudden and accidental. It is only since the invention of the contraceptive pill that pregnancy has become an optional result of intercourse. Before that it was pretty much a certainty that sooner or later a baby would appear. However, pregnancy was still very often a surprise when it occurred, and not something carefully planned.