etta is a Quenya conjunction meaning "therefore".
Perhaps from et and ta. In this case, the possible literal meaning is *"out of which".
 See also
- ↑ J.R.R. Tolkien, "Eldarin Hands, Fingers & Numerals and Related Writings — Part Three" (edited by Patrick H. Wynne), in Vinyar Tengwar, Number 49, June 2007, p. 12