adj

• (botany) Having only one rank or row of petals.
• (obsolete) Simple and honest; sincere, without deceit.
  "Therefore, when thyne eye is single: then is all thy boddy full off light. Butt if thyne eye be evyll: then shall all thy body be full of darknes?"
• (obsolete) Simple; foolish; weak; silly.
  "He utters such single matter in so infantly a voice."

noun

• (music) A 45 RPM vinyl record with one song on side A and one on side B.
• (music) A popular song released and sold (on any format) nominally on its own though usually having at least one extra track.
  "The Offspring released four singles from their most recent album."
• (cricket) A score of one run.
  "He refused to take a single as the ball was dropped by his opponent's best fielder."
• (baseball) A hit in baseball where the batter advances to first base.

verb

• (baseball) To get a hit that advances the batter exactly one base.
  "Pedro singled in the bottom of the eighth inning, which, if converted to a run, would put the team back into contention."
• (agriculture) To thin out.
  "Paul went joyfully, and spent the afternoon helping to hoe or to single turnips with his friend."
• (of a horse) To take the irregular gait called singlefoot.
  "Many very fleet horses, when overdriven, adopt a disagreeable gait, which seems to be a cross between a pace and a trot, in which the two legs of one side are raised almost but not quite, simultaneously. Such horses are said to single, or to be single-footed."
• (intransitive, archaic) To sequester; to withdraw; to retire.
  "an agent singling itself from consorts"