Shelf  n. (pl. Shelves) 1 wooden etc. Board projecting from a wall, or as part of a unit, used to store things. 2 a projecting horizontal ledge in a cliff face etc. B reef or sandbank.  on the shelf 1 (of a woman) regarded as too old to hope for marriage. 2 (esp. Of a retired person) put aside as if no longer useful. [low german]