Apparently a primary word; a "root" (literally or figuratively) -- root.
1. a root: properly, Matthew 3:10; Luke 3:9; ἐκ ῤιζῶν, from the roots (cf. Winer's Grammar, § 51, 1 d.), Mark 11:20; ῤίζαν ἔχειν, to strike deep root, Matthew 13:6; Mark 4:6; tropically, οὐ ῤίζαν ἔχειν ἐν ἑαυτῷ, spoken of one who has but a superficial experience of divine truth, has not permitted it to make its way into the inmost recesses of his soul, Matthew 13:21; Mark 4:17; Luke 8:13; in figurative discourse, ῤίζα πικρίας (see πικρία) of a person disposed to apostatize and induce others to commit the same offence, Hebrews 12:15; the progenitors of a race are called ῤίζα, their descendants κλάδοι (see κλάδος, b.), Romans 11:16-18. Metaphorically, cause, origin, source: πάντων τῶν κακῶν, 1 Timothy 6:10; τῆς σοφίας, Sir. 1:6 (5), 20 (18); τῆς ἀθανασίας, Wis. 15:3; τῆς ἁμαρτίας, of the devil, Ev. Nicod. 23; ἀρχή καί ῤίζα παντός ἀγαθοῦ, Epicur. quoted in Atlmn. 12, 67, p. 546f; πηγή καί ῤίζα καλοκἀγαθίας τό νομίμου τυχεῖν παιδείας, Plutarch, de purr. educ. c. 7 b.