Thank you, all teachers.....
I wonder which word I could use "just in case" or "lest"in the sentece below. I've heard that "lest...should" is rare in modern English.
I had to grab the iron rail at my side （ ） I should slip off and fall.
'Lest' is rare, but in this sentence, it works better to me- it has the meaning of 'for fearb that', which fits better with 'had to', suggesting that a need arose. If it just said 'grabbed', then 'in case' would be fine.