difficult

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

• adjective Requiring considerable effort or skill; not easy to do or accomplish.
• adjective Not easy to endure; full of hardship or trouble; trying.
• adjective Not easy to comprehend, solve, or explain.
• adjective Not easy to please, satisfy, or manage.
• adjective Not easy to persuade or convince; stubborn.

from The Century Dictionary.

• To make difficult; impede.
• To perplex; embarrass.
• Not easy; requiring or dependent on effort; hard; troublesome; arduous.
• Hard to do, perform, or overcome; attended with labor, pains, or opposition; laborious: as, a difficult undertaking.
• Hard to please or satisfy; not compliant; unaccommodating; rigid; austere: as, a person of difficult temper.
• Hard to persuade or induce; stubborn in yielding; obstinate as to opinion: as, he was difficult to convince.
• Hard to understand or solve; perplexing; puzzling: as, a difficult passage in an author; a difficult question or problem.
• Synonyms Difficult, Hard, Arduous (see arduous), laborious, toilsome; obscure, knotty.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb rare To render difficult; to impede; to perplex.
• adjective Hard to do or to make; beset with difficulty; attended with labor, trouble, or pains; not easy; arduous.
• adjective Hard to manage or to please; not easily wrought upon; austere; stubborn.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective hard, not easy, requiring much effort
• adjective hard to manage, uncooperative, troublesome; eg. said of a person, a horse, etc.
• verb obsolete, transitive To make difficult; to impede; to perplex.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective hard to control
• adjective not easy; requiring great physical or mental effort to accomplish or comprehend or endure