IPA: /ˈreɪlər/
KK: /ˈreɪlər/
A person or device that helps to lift or put back on track small trains that have come off the rails.
The railer was used to get the derailed train back on track.
Railers are derived from 'rail' (from Old French *raille*, meaning to mock or jest) and '-er' (meaning a person who). A railer is a person who mocks or criticizes others, often in a scornful manner.
Think of someone who 'mocks' ('rail') others — the '-er' indicates that this person is doing the action. A railer is someone who mocks or criticizes.