Vap \Vap\ (v[a^]p), n. [See Vapid.]

That which is vapid, insipid, or lifeless; especially, the lifeless part of liquor or wine. [Obs.]

In vain it is to wash a goblet, if you mean to put into it nothing but the dead lees and vap of wine. --Jer. Taylor.

Source: Webster's Revised Unabridged Dictionary (1913)