DEFINITION: To collect; with derivatives meaning “to speak.” Oldest form *le-, becoming *leg- in centum languages.
3. lexicon, logion, –logue, –logy; alexia, analects, anthology, catalog, dialect, dialogue, dyslexia, eclectic, eclogite, eclogue, horologe, lectotype, prolegomenon, from Greek legein, to gather, speak, with o-grade derivative logos, a gathering, speech (see also 6 below for derivatives independently built to logos).
Initially, I was researching the etymology of the suffix -logy.
What connects the Greek legein with the PIE root leg-?
My guess is this: In Ancient Greek, if one wanted to speak to many people, then these people must be gathered together. I doubt my guess, because I am unsure if the sense of collection refers to some historical particularity of speech, such as the collection of certain rhetoric. My doubt is worsened by my former ignorance of early ways of reading, when I asked this question on ELU.