Source : Webster's Revised Unabridged Dictionary (1913)

Unbosom \Un*bos"om\, v. t. [imp. & p. p. {Unbosomed}; p. pr. &
   vb. n. {Unbosoming}.] [1st pref. un- + bosom.]
   To disclose freely; to reveal in confidence, as secrets; to
   confess; -- often used reflexively; as, to unbosom one's
   self. --Milton.