Etymology
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null (adj.)

"void of legal force, invalid," 1560s, from French nul, from Latin nullus "not any, none," from ne- "not, no" (from PIE root *ne- "not") + illus "any," diminutive of unus "one" (from PIE root *oi-no- "one, unique").

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nugatory (adj.)

"trifling, of no value; invalid, futile," c. 1600, from Latin nugatorius "worthless, trifling, futile," from nugator "jester, trifler, braggart," from nugatus, past participle of nugari "to trifle, jest, play the fool," from nugæ "jokes, jests, trifles," a word of unknown origin.

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nullify (v.)

"render legally null and void, render invalid," 1590s, from Late Latin nullificare "to esteem lightly, despise," literally "to make nothing," from Latin nullus "not any" (see null) + combining form of facere "to make" (from PIE root *dhe- "to set, put"). Related: Nullified; nullifying; nullifier.

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confute (v.)

"prove to be false or invalid, overthrow by evidence or stronger argument," 1520s, from French confuter, from Latin confutare "repress, check; disprove, restrain, silence," from assimilated form of com-, here perhaps an intensive prefix (see con-), + *futare "to beat," which is perhaps from PIE root *bhau- "to strike." Related: Confuted; confuting.

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fallacy (n.)
late 15c., "deception, false statement," from Latin fallacia "deception, deceit, trick, artifice," abstract noun from fallax (genitive fallacis) "deceptive," from fallere "deceive" (see fail (v.)). Specific sense in logic, "false syllogism, invalid argumentation," dates from 1550s. An earlier form was fallace (c. 1300), from Old French fallace.
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void (adj.)
c. 1300, "unoccupied, vacant," from Anglo-French and Old French voide, viude "empty, vast, wide, hollow, waste, uncultivated, fallow," as a noun, "opening, hole; loss," from Latin vocivos "unoccupied, vacant," related to vacare "be empty," from PIE *wak-, extended form of root *eue- "to leave, abandon, give out." Meaning "lacking or wanting" (something) is recorded from early 15c. Meaning "legally invalid, without legal efficacy" is attested from mid-15c.
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putative (adj.)

"supposed, reputed, commonly thought of or deemed," early 15c., from Late Latin putativus "supposed," from putat-, past-participle stem of Latin putare "to judge, suppose, believe, suspect," originally "to clean, trim, prune" (from PIE root *pau- (2) "to cut, strike, stamp"). At first especially in putative marriage, one which, though legally invalid due to an impediment, was contracted in good faith by at least one party. Related: Putatively.

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vain (adj.)
c. 1300, "devoid of real value, idle, unprofitable," from Old French vain, vein "worthless, void, invalid, feeble; conceited" (12c.), from Latin vanus "empty, void," figuratively "idle, fruitless," from PIE *wano-, suffixed form of root *eue- "to leave, abandon, give out."

Meaning "conceited, elated with a high opinion of oneself" first recorded 1690s in English; earlier "silly, idle, foolish" (late 14c.). Phrase in vain "to no effect" (c. 1300, after Latin in vanum) preserves the original sense. Related: Vainly; vainness. Compare also vainglory.
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pabulum (n.)

"food" for anything, "food" in its widest sense, "that which nourishes an animal or vegetable," 1670s, from Latin pabulum "fodder, food, nourishment," from PIE root *pa- "to feed" + instrumentive suffix *-dhlom. Related Pabular; pabulary; pabulous.

Pablum (1932), derived from this, is a trademark (Mead Johnson & Co.) for a soft, bland cereal used as a food for infants and weak and invalid persons, hence its figurative use (attested from 1970, first by U.S. Vice President Spiro Agnew) in reference to "mushy" political prose.

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Anabaptist (n.)
class of Christians who regard infant baptism as invalid, 1530s, literally "one who baptizes over again," from Modern Latin anabaptista, from Late Latin anabaptismus "second baptism" (used in literal sense from 4c.), from Ecclesiastical Greek anabaptismos, from ana "again, anew" (see ana-) + baptismos "baptism" (see baptism).

Originally in English in reference to the sects that practiced adult baptism and arose in Germany from 1521. Probably so called because, as a new faith, they baptized converts who already had been baptized (as infants) in the older Catholic or older Protestant churches. Modern branches (notably Mennonites and Amish) baptize only once (adults) and do not actively seek converts. The name also was applied, usually opprobriously, to Baptists, perhaps due to the multiple immersions of their baptisms.
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