lecture vs talk

lecture and talk both are nouns.

Word	Noun	Adjective	Verb	Adverb
lecture	Yes	No	Yes	No
talk	Yes	No	Yes	No

As nouns, talk is a hyponym of lecture; that is, talk is a word with a more specific, narrower meaning than lecture:

lecture: teaching by giving a discourse on some subject (typically to a class)
talk: the act of giving a talk to an audience

As nouns, lecture and talk are synonyms defined as:

Other synonyms of lecture include public lecture.

As verbs, lecture and talk are synonyms defined as:

lecture (noun)	talk (noun)
teaching by giving a discourse on some subject (typically to a class)	the act of giving a talk to an audience
a speech that is open to the public	an exchange of ideas via conversation
a lengthy rebuke	idle gossip or rumor
	a speech that is open to the public
	discussion; (`talk about' is a less formal alternative for `discussion of')

lecture (verb)	talk (verb)
censure severely or angrily	express in speech
deliver a lecture or talk	exchange thoughts; talk with
	reveal information
	use language
	deliver a lecture or talk
	divulge confidential information or secrets