- billfold (n.)
- 1879, from bill (n.1) + fold, here perhaps short for folder.
- biomass (n.)
- also bio-mass, c. 1980, from bio- + mass (n.1).
- bitty (adj.)
- "small," 1873, baby-talk, from bit (n.1) + -y (2).
- blithesome (adj.)
- 1724, from blithe + -some (1). An adjective from an adjective. Related: Blithesomely; blithesomeness.
- blowhole (n.)
- also blow-hole, 1787, of whales and porpoises, from blow (v.1) + hole.
- uninhabited (adj.)
- 1570s, from un- (1) "not" + past participle of inhabit (v.).
- fireball (n.)
- also fire-ball, 1550s, from fire (n.) + ball (n.1).
- worrisome (adj.)
- "causing worry or annoyance," 1828, from worry + -some (1). Related: Worrisomely.
- unabashed (adj.)
- 1570s, from un- (1) "not" + past participle of abash (v.). Related: Unabashedly.
- unadulterated (adj.)
- 1719, from un- (1) "not" + past participle of adulterate (v.).
- unannounced (adj.)
- 1775, from un- (1) "not" + past participle of announce (v.).
- unanticipated (adj.)
- 1741, from un- (1) "not" + past participle of anticipate (v.).
- unappreciated (adj.)
- 1809, from un- (1) "not" + past participle of appreciate (v.).
- unappreciative (adj.)
- 1834, from un- (1) "not" + appreciative. Related: Unappreciatively; unappreciativeness. Inappreciative is from 1849.
- unassailable (adj.)
- 1590s, from un- (1) "not" + assailable (see assail (v.)). Related: Unassailably.
- unbeknown (adj.)
- "unknown," 1630s, from un- (1) "not" + beknown (see beknow).
- uncensored (adj.)
- 1890, from un- (1) "not" + past participle of censor (v.).
- unchanging (adj.)
- 1590s, from un- (1) "not" + present participle of change (v.).
- uncharted (adj.)
- 1804, from un- (1) "not" + past participle of chart (v.).
- unchartered (adj.)
- 1805, from un- (1) "not" + past participle of charter (v.).
- unchivalrous (adj.)
- 1814, from un- (1) "not" + chivalrous. Related: Unchivalrously; unchivalric.
- uncivil (adj.)
- 1550s, "barbarous," from un- (1) "not" + civil (adj.). Meaning "impolite" is 1590s.
- uncomprehending (adj.)
- 1795, from un- (1) "not" + present participle of comprehend (v.). Related: Uncomprehendingly.
- uncomprehensible (adj.)
- late 14c., from un- (1) "not" + comprehensible. The usual word is incomprehensible.
- uncompromised (adj.)
- 1775, from un- (1) "not" + past participle of compromise (v.).
- unconformity (n.)
- c. 1600, from un- (1) "not" + conformity. Geological sense is from 1829.
- unconstrained (adj.)
- 1640s, from un- (1) "not" + past participle of constrain (v.). Related: Unconstrainedly.
- uncountable (adj.)
- late 14c., from un- (1) "not" + count (v.) + -able.
- uncredited (adj.)
- 1580s, from un- (1) "not" + past participle of credit (v.).
- unremitted (adj.)
- 1640s, from un- (1) "not" + past participle of remit (v.).
- unremitting (adj.)
- 1728, from un- (1) "not" + present participle of remit (v.). Related: Unremittingly.
- unrepairable (adj.)
- 1610s, from un- (1) "not" + repairable (adj.). Related: Unrepairably.
- unrivalled (adj.)
- also unrivaled, 1590s, from un- (1) "not" + past participle of rival (v.).
- unsatisfactory (adj.)
- 1640s, from un- (1) "not" + satisfactory (adj.). Related: Unsatisfactorily; unsatisfactoriness.
- unsecured (adj.)
- 1780, from un- (1) "not" + past participle of secure (v.).
- unsentimental (adj.)
- 1752, from un- (1) "not" + sentimental (adj.). Related: Unsentimentally.
- unstoppable (adj.)
- 1827; see un- (1) "not" + stop (v.) + -able.
- unsubsidized (adj.)
- 1756, from un- (1) "not" + past participle of subsidize (v.).
- unsubstantiated (adj.)
- 1775, from un- (1) "not" + past participle of substantiate (v.).
- unsuitable (adj.)
- 1590s, from un- (1) "not" + suitable (adj.). Related: Unsuitably; unsuitability.
- unsullied (adj.)
- 1580s, from un- (1) "not" + past participle of sully (v.).
- unsurmountable (adj.)
- "incapable of being overcome," 1701, from un- (1) "not" + surmountable.
- unsurpassable (adj.)
- 1610s, from un- (1) "not" + surpassable (see surpass (v.)).
- unsurpassed (adj.)
- 1775, from un- (1) "not" + past participle of surpass (v.).
- unsuspecting (adj.)
- 1590s, from un- (1) "not" + present participle of suspect (v.).
- unswerving (adj.)
- 1690s, from un- (1) "not" + present participle of swerve (v.).
- untenanted (adj.)
- 1670s, from un- (1) "not" + tenanted (see tenant (n.)).
- untrammeled (adj.)
- also untrammelled, 1795, from un- (1) "not" + past participle of trammel (v.).
- unvanquished (adj.)
- late 14c., from un- (1) "not" + past participle of vanquish (v.).
- unwavering (adj.)
- 1560s, from un- (1) "not" + present participle of waver (v.).
