underside

From under- +‎ side.

• (US) IPA^(key): /ˈʌndɚsaɪd/

underside (plural undersides)

1. The side that is below or underneath, the bottom.
   • 1944 May and June, “Notes and News: Tank Engine Stability”, in Railway Magazine, page 185:

     A correspondent suggested that the superior riding qualities of the latter were due to the absence of piston-valve chests above the cylinders, which made it possible to bring the underside of the water-tanks to a lower level than that of the "Rivers", so minimising the unsteadying effect of water surging in the tanks.

   • 1963 March, “The Clacton express electric multiple-units enter service”, in Modern Railways, page 173:

     [...] and the neat reading lamps on the underside of the luggage racks, under passenger control, are an attractive feature of the first class compartments.

   • 2016 January 23, Michael Emons, “Crystal Palace 1–3 Tottenham”, in BBC Sport‎:

     The Eagles then hit the woodwork twice in a matter of seconds as Scott Dann headed Jason Puncheon's free-kick against the underside of the bar, before substitute Mile Jedinak also hit the crossbar with a shot on the turn.

• overside

• undesired

From under- +‎ side.

underside f or m (definite singular undersida or undersiden, indefinite plural undersider, definite plural undersidene)

1. underside

• overside

• “underside” in The Bokmål Dictionary.

From under- +‎ side.

underside f (definite singular undersida, indefinite plural undersider, definite plural undersidene)

1. underside

• overside

• “underside” in The Nynorsk Dictionary.