【Speech】 ,  【address】 ,  【oration】 ,  【harangue】 ,  【lecture】 ,  【talk】 ,  【sermon】 ,  【homily】  designate a discourse delivered to an audience.

【Speech】 can apply to a public discourse irrespective of its quality or its degree of preparation, of its aim (as to influence, instruct, or entertain), or of the caliber of its speaker or audience.

【Address】 implies formality and usually careful preparation; it often connotes distinction in the speaker or gives emphasis to the importance of the 【speech】 .

【Oration】 suggests eloquence, rhetorical style, and usually a dignified but sometimes a high-flown or long-winded appeal to the emotions of a large audience or assembly.

【Harangue】 , once nearly equivalent to  【oration】 except for its added implications of vehemence and passion, commonly retains only these distinctive implications and connotes either length and tediousness of 【speech】 or an impassioned appeal to the audience.

【Lecture】 often implies reading; it commonly designates a carefully prepared 【speech】 on a special topic intended to give information and instruction to a group of students or studious persons.

【Talk】 stresses informality; it may be used to designate either a 【lecture】 or an 【address】 when the speaker wishes to emphasize his desire to speak directly and simply to his auditors as individuals.

【Sermon】  and  【homily】  both commonly imply religious instruction by an ordained preacher and a church congregation as the listeners; in such use  【sermon】  usually connotes a theme drawn from a scriptural text, while  【homily】 suggests practical moral counsel rather than doctrinal discussion. But both terms have extended use in which they denote a usually didactic 【talk】 or discussion on a moral theme.