So, how hard is it, really, to file those tax returns? The adjectives grueling and taxing both describe activities or experiences that are tiring and difficult. We tend to reserve the adjective grueling for activities or experiences that are extremely difficult to complete or endure (the grueling Boston Marathon; a grueling schedule), to the point of being severe or punishing. Something that is taxing wears on a person gradually, by the demands it makes on the body, mind, or emotions (the most emotionally taxing role of the actor’s career). The word taxing is more amenable to qualification—something could be a bit taxing or extremely taxing, whereas grueling is pretty much an all-or-nothing adjective.
The verbs agree and concur both mean to have the same opinion as another. However, agree often presupposes an interpersonal process by which this harmony is reached. The context might involve discussion and negotiation (they agreed on a theme for the party), or consent or compliance (agree to a pay cut) between the parties. To concur, on the other hand, is to show accord in matters of opinion, as of minds that have independently run along the same channels (to concur in a judgment about a painting). It would be unusual to say, “I concur with you,” not only because concur is a more formal word choice than agree, but also because concurring is more impersonal: one doesn’t usually concur with a person but with the substance of an opinion or judgment.
As a simple negative of happy, the adjective unhappy has a fairly broad range of application. A person described as unhappy may be sad or miserable, or they may simply be displeased or discontented with one particular thing, as when one is unhappy with the outcome of something. The word miserable, on the other hand, leaves less room for interpretation. A miserable person is intensely unhappy, to a pitiable degree. Where miserable comes in especially useful is in describing a wretched state or condition, such as a miserable cold, a miserable pregnancy, miserable weather, miserable living conditions, or, worst of all, a miserable existence. Miserable is a more feeling word than unhappy, and carries a strong element of the pathetic. As with all things pathetic or wretched, it can evoke either pity or contempt. For example, there’s no empathy in calling someone “a miserable so and so”: for miserable here you could just as well substitute lowdown or despicable.