Most Tibetan scholars seem to have taken for granted that lo tsā ba is a contraction (or rather corruption) of Sanskrit lokacakṣu and hence rendered as ’jig rten mig (“eye of the world”) or occasionally also as ’jig rten mig ’byed (“eye-opener of the world”). Professor Michael Hahn in our recent Symposium on “Cross-Cultural Transmission of Buddhist Texts: Theories and Practices of Translation” (http://www.kc-tbts.uni-hamburg.de/index.php/en/workshops-conferences), however, pointed out that lo tsā ba and lo mi tsā ba can well be words like tha dad pa and tha mi dad pa (see our entry here), the meanings of which have long been forgotten. But he did not elaborate on this. I suggested that lo in lo tsā ba might mean “language,” to which he commented: “Even better.” I am sure he has something more up his sleeves. We shall have to wait and see.
But in the mean time, I thought of making a wild speculation (in support of Hahn’s theory). First, as I suggested Hahn, I would assume that lo means “language.” Second, what could have tsā ba and mi tsā ba once meant? I speculate that tsā ba is a derivation or corruption of cha ba meaning “to know or to be knowledgeable.” See the brDa rnying tshig mdzod (p. 403), where myi cha ba is said to mean “not to know or not to be knowledgeable” (mi shes pa). See also the Tshig mdzod chen mo (s.v.). Is there an expression in Tibetan that runs something like: ya mi cha ba? One needs to check on this. So according to this speculation lo tsā ba is “one who is knowledgeable about languages” and lo mi tsā ba is “one who is not knowledgeable about languages.” So much for now.
Beckwith is said to have suggested that the word lo tsā ba is perhaps somehow connected with the Old Newari littsāvi (liccāvi). See Verhagen 2010 (i.e. “Notes Apropos…”): 466, n. 466, n. 5. But meaning what?