hard

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Resistant to pressure; not readily penetrated; firm or solid.
• adjective Well protected from an attack, as by aerial bombardment.
• adjective Requiring great effort or endurance.
• adjective Performed with or marked by great diligence or energy.
• adjective Difficult to resolve, accomplish, or finish.
• adjective Difficult to understand or impart.
• adjective Proceeding or performing with force, vigor, or persistence; assiduous.
• adjective Intense in force or degree.
• adjective Inclement or severe.
• adjective Stern, strict, or demanding.
• adjective Lacking compassion or sympathy; callous.
• adjective Difficult to endure; causing hardship or suffering.
• adjective Oppressive or unjust in nature or effect.
• adjective Harsh or severe in effect or intention.
• adjective Marked by stubborn refusal to compromise or yield; uncompromising.
• adjective Bitter or resentful.
• adjective Showing disapproval, bitterness, or resentment.
• adjective Causing damage or premature wear.
• adjective Bad; adverse.
• adjective Real and unassailable.
• adjective Definite; firm.
• adjective Free from illusion or sentimentality; practical or realistic.
• adjective Using or based on data that are readily quantified or verified.
• adjective Marked by sharp delineation or contrast.
• adjective Lacking in shade; undiminished.
• adjective Hardcore.
• adjective Being a turn in a specific direction at an angle more acute than other possible routes.
• adjective Metallic, as opposed to paper. Used of currency.
• adjective Backed by bullion rather than by credit. Used of currency.
• adjective High and stable. Used of prices.
• adjective Durable; lasting.
• adjective Written or printed rather than stored in electronic media.
• adjective Erect; tumid. Used of a penis.
• adjective Having high alcoholic content; intoxicating.
• adjective Rendered alcoholic by fermentation; fermented.
• adjective Containing dissolved salts that interfere with the lathering action of soap. Used of water.
• adjective Linguistics Velar, as in c in cake or g in log, as opposed to palatal or soft.
• adjective Physics Of relatively high energy; penetrating.
• adjective High in gluten content.