Solitarily comes from solitary + -ly. Solitary derives from Latin sōlitārius ('alone, lonely'), from sōlitās ('loneliness'), from sōlus ('alone'). The historical chain includes Latin sōlitārius and Latin sōlus. The quoted older senses, "alone, lonely", "loneliness", and "alone", supply the semantic anchors for solitarily. The formation is best read as suffixal and borrowed: the word solitarily carries its older form-history into a compact English lexical shape. In present English it is used as a adv, "in a solitary manner; alone and without company". Related English forms include solitary, solitude, and solitaire. The result is a adv whose etymology preserves both the older form and the later English specialization.