talk vs lecture

talk and lecture both are nouns.

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

As nouns, lecture is a hypernym of talk; that is, lecture is a word with a broader meaning than talk:

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

Other hypernyms of talk include lecturing.

As nouns, talk and lecture are synonyms defined as:

Other synonyms of talk include public lecture.

As verbs, talk and lecture are synonyms defined as:

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

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