These words describe intense states of desire, dedication or conviction. Passionate and impassioned , both drawn from a word meaning to suffer, are most commonly used for states of desire, with a strong overtone of sexuality. Impassioned is the more inward and passive and less ambiguous of the two when applied to people, suggesting deep and abiding feeling. Passionate is less lofty in tone and suggests that the desire is more a matter of appetite.

• Their quiet hour by the fire had filled her with such impassioned tenderness that she was quite alarmed by his passionate advances.

Passionate may even suggest a lack of discrimination: Passionate as he was, he had never truly loved any of his many paramours. It may, of course, be used without suggesting such negative connotations: Lawrence preferred the passionate to the rational life. When applied to the effective expression of strong feeling, impassioned is the more usual choice: an impassioned speech.

Ardent , fiery and burning describe intense feeling in terms of fire. Of these, only ardent is free of negative implications in describing both desire and dedication: an ardent lover; an ardent patriot. Fiery would not be useful to describe states of desire, except for poetic effect, in which case it might be thought cliché: fiery embraces. In describing dedication, it suggests angry rather than impassioned conviction, and even wildness or instability: fiery demagogue; fiery denunciation. Burning , for both desire and dedication, has become a high-level cliché, avoided by some thoughtful writers: burning passion; burning issues.

Fervent and fervid come from the same root, meaning to boil. Their relationship is somewhat like that of impassioned and passionate . Fervent , like impassioned , implies being filled with abiding feeling; fervid , an intensification of fervent , suggests feverish intensity and a greater compulsion to act, with the same negative overtones possible as for passionate . Both fervent and especially fervid, have become somewhat stilted in tone.

Zealous and vehement are both more applicable to dedication than to desire. One might perhaps speak of a zealous lover, but hardly of a vehement one. Zealous , most strictly, refers to intense religious conviction, although it applies as well to unwavering adherence to any set of beliefs or attitudes: a zealous convert; a zealous rock ‘n’ roll fan. The word suggests that one is prepared to act on one’s beliefs unthinkingly, without question. This gives a strong negative overtone of one-sided fanaticism: the zealous , witch-burning citizens of Salem. Vehement, even more strongly than zealous , implies belligerence and challenge, but, unlike zealous , it is more often applied to things or attitudes than to people: a vehement reply; a vehement gesture; he was downright vehement about racial intolerance.