an obstruction that stands in the way (and must be removed or surmounted or circumvented)
something immaterial that stands in the way and must be circumvented or surmounted; "lack of imagination is an obstacle to one's advancement"; "the poverty of a district is an obstacle to good education"; "the filibuster was a major obstruction to the success of their plan"
small densely furred aquatic monotreme of Australia and Tasmania having a broad bill and tail and webbed feet; only species in the family Ornithorhynchidae
the magnitude of sound (usually in a specified direction); "the kids played their music at full volume"
a publication that is one of a set of several similar publications; "the third volume was missing"; "he asked for the 1989 volume of the Annual Review"
the amount of 3-dimensional space occupied by an object; "the gas expanded to twice its original volume"
a relative amount; "mix one volume of the solution with ten volumes of water"
any warm-blooded vertebrate having the skin more or less covered with hair; young are born alive except for the small subclass of monotremes and nourished with milk