I. ˈ ̷ ̷ ̷ ̷ˌ ̷ ̷ ̷ ̷ noun
Etymology: under (III) + lining
: lining placed on the under or the inner side of something
II. noun
Etymology: from gerund of underline (II)
: the action of drawing lines underneath in writing or printing or lines so drawn : underscoring
letters … with their underlinings and broken sentences and postscripts — G.H.Genzmer