(n): use of physical or mental energy; hard work
(n): a factor causing trouble in achieving a positive result or tending to produce a negative result
(n): something immaterial (as a circumstance or influence) that contributes to producing a result
(n): a condition or state of affairs almost beyond one's ability to deal with and requiring great effort to bear or overcome
(n): a state at a particular time
(n): the quality of being difficult
(n): an essential and distinguishing attribute of something or someone
