[pathetic]. From the Greek word "pathos" meaning "suffering." Compare pathos, sympathy, pathology, electropathy, allopathy, homœopathy.
[dilapidated]. From the Latin "lapis" meaning a "stone." It probably means to separate stone from stone. Compare lapidary, dilapidation.
[intermediate]. From the Latin "medius" meaning "middle." Compare mediate, immediate, medium, mediocrity, mediator.
[police]. From the Greek "polis" meaning a "city." Compare politics, policy, metropolis, politician.
[barrister]. From the word "bar." There was a bar in the law court, from which the lawyer pleaded his case. So the pleader was called a bar-ister. Compare the phrase "called to the Bar."
[obstacle]. From the Latin root "sta-" meaning to stand. Compare obstinate, station, status, statute, instant, distance, constant.
[dastardly]. A word of doubtful origin,—probably akin to the word "dazed."
[reality]. From the Latin word "res" meaning a "thing." Compare real, unreal, realize, republic, really, realization.
[alternated]. From the Latin "alter" meaning "other." Compare alteration, alternative, alter, altercate.
[infinity]. From the Latin "finis" meaning "end." Compare finish, finite, definite, confine.