WordNet sense 1 (any of various water-soluble compounds capable of turning litmus blue and reacting with an acid to form a salt and water):

alkali

WordNet sense 2 (the most important or necessary part of something):

threaten

WordNet sense 3 ((numeration system) the positive integer that is equivalent to one in the next higher counting place):

radix

WordNet sense 4 (the place where you are stationed and from which missions start and end):

home

WordNet sense 5 (a terrorist network intensely opposed to the United States that dispenses money and logistical support and training to a wide variety of radical Islamic terrorist groups; has cells in more than 50 countries):

al-Qaeda, al-Qaida, al-Qa'ida, Qaeda

WordNet sense 6 (a lower limit):

floor

WordNet sense 7 ((linguistics) the form of a word after all affixes are removed):

radical, root, stem, theme, root word

WordNet sense 8 (the fundamental assumptions from which something is begun or developed or calculated or explained):

cornerstone, foundation, groundwork, fundament

WordNet sense 9 (the stock of basic facilities and capital equipment needed for the functioning of a country or area):

infrastructure

WordNet sense 10 (lowest support of a structure):

foot, substructure, understructure

WordNet sense 11 (installation from which a military force initiates operations):

base of operations

WordNet sense 12 (place that runner must touch before scoring):

bag

WordNet sense 13 (a support or foundation):

pedestal, stand

WordNet sense 14 (not adhering to ethical or moral principles):

dishonorable, immoral, unethical, dishonourable

WordNet sense 15 (serving as or forming a base):

basal

WordNet sense 16 (pertaining to or constituting a base or basis):

basic

WordNet sense 17 (of low birth or station (`base' is archaic in this sense)):

humble, lowly, baseborn

WordNet sense 18 (of humble birth or origins):

lowborn

WordNet sense 19 (having or showing an ignoble lack of honor or morality):

mean, meanspirited

WordNet sense 20 (completely lacking nobility in character or quality or purpose):

ignoble

WordNet sense 21 (not genuine; imitating something superior):

counterfeit, imitative

WordNet sense 22 (assign to a station):

place, post, send, station

WordNet sense 23 (use (purified cocaine) by burning it and inhaling the fumes):

free-base

WordNet sense 24 (use as a basis for; found on):

ground, establish, found