1. The back part or rear of anything.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• backsing,
• backsided,
• backsd,
• backsit,
• lakside,
• badside,
• backlite,
• baside,
• backsaide,
• bakside,
• bakcside,
• backsied,
• back side,
• banksiede,
• banksied,
• Barmeside,
• acklide,
• backsoo,
• bacifide,
• Backsinue

• baked,
• Baskett,
• basket,
• backseat,
• backstay,
• backed.

The adjective form of "backside" is "backside" itself. It can function as both a noun and an adjective.

The plural of the "backside" can be the "backsides".

The singular of the "backside" can be the "backside".