'Third rail' definitions:
Definition of 'third rail'
From: WordNet
noun
A rail through which electric current is supplied to an electric locomotive
Definition of 'Third rail'
From: GCIDE
- Third rail \Third rail\ (Electric Railways) (a) The third rail used in the third-rail system. (b) An electric railway using such a rail. [Colloq.] [Webster 1913 Suppl.]