Digamma

dī-gam′ma, n. an obsolete letter of the Greek alphabet, having the force of our W. [So called from its form ( IMG:c224_ers_1908_Digamma.png_utm_source_en.wiki source.org_utm_campaign_parser_utm_content_thumbnail_unscaled:Chambers_1908_Digamma.png?utm_source=en.wiki source.org _campaign=parser _content=thumbnail_unscaled ), like one capital Γ (gamma) placed over another.]