Definition of "their"
their
determiner
Belonging to, from, of, or relating to, them (plural).
Quotations
For all things, even Celestial Luminaries, much more atmospheric meteors, have their rise, their culmination, their decline.
1831, Thomas Carlyle, “Symbols”, in Sartor Resartus: The Life and Opinions of Herr Teufelsdröckh. […], London: Chapman and Hall, […], book third, page 155
Since the launch early last year of […] two Silicon Valley start-ups offering free education through MOOCs, massive open online courses, the ivory towers of academia have been shaken to their foundations. University brands built in some cases over centuries have been forced to contemplate the possibility that information technology will rapidly make their existing business model obsolete.
2013 July 20, “The attack of the MOOCs”, in The Economist, volume 408, number 8845
Belonging to someone (one person, singular), or occasionally to something.
Quotations
There's not a man I meet but doth salute meAs if I were their well-acquainted friend […]
c. 1594 (date written), William Shakespeare, “The Comedie of Errors”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act IV, scene iii], line 1172
‘I mean ... if somebody made a mistake,’ Harry went on, ‘and let something slip, I know they didn’t mean to do it. It’s not their fault,’ he repeated, again a little louder than he would usually have spoken.
2007, J. K. Rowling, Harry Potter and the Deathly Hallows, (quoted edition: London: Bloomsbury, 2008, page 93)
adverb
contraction