【Lucky】 , 【fortunate】 ,  【happy】 ,  【providential】  all mean meeting with or producing a favorable outcome or an unforeseen or unpredictable success.

【Lucky】 implies that the person or persons involved have been favored by chance and that the success has not been the result of merit or merits.

【Fortunate】 , although it is often indistinguishable from  【lucky】  in its implications, is more formal and more likely to suggest an unanticipated absence of all handicaps and mischances or presence of such favorable circumstances as might argue the intervention of a higher power (compare fortune under CHANCE 1 ) that watches over one.

【Happy】  differs from the preceding words chiefly in its combining the meaning of  【lucky】  or  【fortunate】  with that of its more common sense of being blessed or made glad (see GLAD ); thus, a  【happy】  outcome is not only one that is 【fortunate】 but one that makes the person affected feel 【happy】 ; a  【happy】 accident is an accidental event or circumstance that brings to light something that proves a treasure.

【Providential】 often carries an implication of good fortune resulting from the help or interference of Providence.

Often, however, the word carries no trace of this implication and means little more than  【lucky】  or  【fortunate】 .