'Retaining wall' definitions:

Definition of 'retaining wall'

noun

A wall that is built to resist lateral pressure (especially a wall built to prevent the advance of a mass of earth)

From: GCIDE

Retain \Re*tain"\ (r[-e]*t[=a]n"), v. t. [imp. & p. p. Retained (r[-e]*t[=a]nd"); p. pr. & vb. n. Retaining.] [F. retainir, L. retinere; pref. re- re- + tenere to hold, keep. See Tenable, and cf. Rein of a bridle, Retention, Retinue.]
1. To continue to hold; to keep in possession; not to lose, part with, or dismiss; to restrain from departure, escape, or the like. "Thy shape invisible retain." --Shak. [1913 Webster]
Be obedient, and retain Unalterably firm his love entire. --Milton. [1913 Webster]
An executor may retain a debt due to him from the testator. --Blackstone. [1913 Webster]
2. To keep in pay; to employ by a preliminary fee paid; to hire; to engage; as, to retain a counselor. [1913 Webster]
A Benedictine convent has now retained the most learned father of their order to write in its defense. --Addison. [1913 Webster]
3. To restrain; to prevent. [Obs.] --Sir W. Temple. [1913 Webster]
Retaining wall (Arch. & Engin.), a wall built to keep any movable backing, or a bank of sand or earth, in its place; -- called also retain wall. [1913 Webster]
Syn: To keep; hold; restrain. See Keep. [1913 Webster]