Sideline

n. line of merchandise that is secondary to the principal line; secondary business or activity; line that marks the boundary on a playing field (Sports); area located immediately outside the boundary on a playing field (Sports)

The "sidelines" is a term commonly used to define the white or colored lines which mark the outer boundaries of a sports field.  American football sidelines, for example, mark the edge of the field. Should a player pass through the sidelines, he is considered out of bounds. The sidelines are also where the coaching staff and players out of play operate during a game.
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Noun
1. a line that marks the side boundary of a playing field
(synonym) out of bounds
(hypernym) line
(hyponym) touchline
2. an auxiliary line of merchandise
(hypernym) line, product line, line of products, line of merchandise, business line, line of business
3. an auxiliary activity
(synonym) avocation, by-line, hobby, spare-time activity
(hypernym) pastime, interest, pursuit
(hyponym) speleology, spelaeology

Synonyms and related words:
avocation, bank, board, border, bordure, brim, brink, brow, by-line, catalog goods, coast, commodities, consumer goods, consumer items, delay, edge, effects, featheredge, flange, frame, fringe, goods, goods for sale, hem, hobby, hobbyhorse, inventory, job lot, labellum, labium, labrum, lay aside, lay away, lay by, ledge, limb, limbus, line, line of goods, lip, list, mail-order goods, marge, margin, merchandise, pastime, pigeonhole, postpone, push aside, put aside, put away, put in mothballs, ragged edge, rim, selvage, set aside, set by, shelve, shore, side, side interest, skirt, spare-time activity, staples, stock, stock-in-trade, store, stow, table, table the motion, vendibles, verge, wares
  

sideline /'saidlain/
ngoại động từ cho ra ngoài, cho ra ngoài lề (không được tham gia vào cuộc đấu...)he was sidelined by his injury: anh ấy bị thương phải cho ra ngoài
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