Noun sideline has 3 senses
  1. sideline, out of bounds - a line that marks the side boundary of a playing field
    --1 is a kind of line
    --1 has particulars: touchline
  2. sideline - an auxiliary line of merchandise
    --2 is a kind of
    line, product line, line of products, line of merchandise, business line, line of business
  3. avocation, by-line, hobby, sideline, spare-time activity - an auxiliary activity
    --3 is a kind of pastime, interest, pursuit
    --3 has particulars: speleology, spelaeology