WordNet sense 1 (a blank character used to separate successive words in writing or printing):

space

WordNet sense 2 (a blank gap or missing part):

lacuna

WordNet sense 3 (a cartridge containing an explosive charge but no bullet):

dummy, blank shell

WordNet sense 4 ((of weapons) not charged with ammunition):

unloaded

WordNet sense 5 ((of a surface) not written or printed on):

clean, white

WordNet sense 6 (holding or containing nothing):

empty

WordNet sense 7 (void of expression):

vacuous

WordNet sense 8 (not inclined to talk or give information or express opinions):

uncommunicative, incommunicative