rail

1 rail /ˈreɪl/ noun
plural rails
1 rail
/ˈreɪl/
noun
plural rails
Britannica Dictionary definition of RAIL
1 
[count]
a  : a bar that goes from one post or support to another and that is used to form a barrier
— see picture at house; see also guardrail, handrail
b  : a bar used to hang something from
2 
a  [count] : one of the bars of steel that form a train's track — usually plural
— see also third rail
b  [noncount] : 1railroad
— often used before another noun
— see also monorail

go off the rails

informal
: to lose control and start to behave in a way that is not normal or acceptable
2 rail /ˈreɪl/ verb
rails; railed; railing
2 rail
/ˈreɪl/
verb
rails; railed; railing
Britannica Dictionary definition of RAIL
[+ object]
: to use rails to create a barrier around or at the edge of (something) — usually + off
3 rail /ˈreɪl/ verb
rails; railed; railing
3 rail
/ˈreɪl/
verb
rails; railed; railing
Britannica Dictionary definition of RAIL
[no object] formal
: to complain angrily about something