Definition of "underframe"

The main fuel tank is slung from the underframe midway between the two bogies, and its capacity of 420 gal. supplies both the main engine and the train heating boiler.

1950 November, “Mixed-Traffic Diesel-Electric Locomotives for Ireland”, in Railway Magazine, page 781

Nos. 5300/1, which were finished in January, are the Southern's first "4-EPB" units to the standard B.R. design on 63 ft. 5 in. underframes, as against the S.R. 62 ft.; [...].

1960 March, “Talking of Trains: S.R. multiple-unit news”, in Trains Illustrated, page 125

The Liner train wagon is a simple underframe on bogies, with coned location points that engage recesses in the container bases.

1964 April, G. Freeman Allen, “The BRB shows traders the Liner train prototypes”, in Modern Railways, page 265