WordNet sense 1 (someone from whom you are descended (but usually more remote than a grandparent)):

ancestor, antecedent, ascendant, ascendent

WordNet sense 2 (the place where something begins, where it springs into being):

beginning, origin, source, rootage

WordNet sense 3 (the set of values that give a true statement when substituted into an equation):

solution

WordNet sense 4 (a simple form inferred as the common basis from which related words in several languages can be derived by linguistic processes):

etymon

WordNet sense 5 ((linguistics) the form of a word after all affixes are removed):

base, radical, stem, theme, root word

WordNet sense 6 (the part of a tooth that is embedded in the jaw and serves as support):

tooth root

WordNet sense 7 (dig with the snout):

rout, rouT, rootle, rout

WordNet sense 8 (take sides with; align oneself with; show strong sympathy for):

pull, side

WordNet sense 9 (become settled or established and stable in one's residence or life style):

settle, steady down, take root, settle down