• obelisk (†)

  • obelism

  • object

  • object complement

  • object pronoun

  • oblique (/)

  • oblique case

  • occlusive

  • OED

  • officialese

  • officious | official

  • of-genitive

  • Ogden, C.K.

  • Ogham

  • Oh | O

  • Old Church Slavonic

  • Old English

  • Old French

  • Old High German

  • Old Low German

  • Old North French

  • Old Saxon

  • oligosynthetic language

  • onomasiology

  • onomasticon

  • onomastics

  • onomatechny

  • onomatology

  • onomatopoeia

  • onomatopoeic coinage

  • onomatotechny

  • onset

  • open-class item

  • open word class

  • optative mood

  • ordinance | ordnance

  • oronyms

  • orthoepy

  • orthographic depth

  • orthographic principle

  • orthography

  • ostensive definition

  • OV language

  • Oxford comma

  • Oxford English Dictionary

  • oxymoron