Barrier n. : A carpentry obstruction, stockade, or other obstacle made in a passage in order to stop an enemy.

Barrier n. : A fortress or fortified town, on the frontier of a country, commanding an avenue of approach.

Barrier n. : A fence or railing to mark the limits of a place, or to keep back a crowd.

Barrier n. : An any obstruction; anything which hinders approach or attack.

Barrier n. : Any limit or boundary; a line of separation.

Example:
What are the four Barriers to building social capital today according to Putnam? What is the largest Barrier a

Taxonomy
Barrier, free encyclopedia, Physical barriers, temporary fencing, flood control, control structure, on the River, the River Thames, England, British Columbia, Canada, the Dutch, search, free dictionary, physical structure, blocks, analogy, block roads, railway crossings.

Defination from the web:
barrier, used to attenuate noise pollution. Road block, a temporary installation to control or block traffic on a road ... Thames Barrier, a flood control structure on the River Thames in England. Separation barrier, a wall or fence which prevents the movement of people across ...