Of persons (conjoined twins) or things: joined together physically.
1580s, Ovid, Elegia VI, Book I, translated by Christopher Marlowe, in Christopher Marlowe: The Complete Poems and Translations, Stephen Orgel (ed.), Penguin, 1971, p. 110,
And farewell cruel posts, rough threshold's block, / And doors conjoined with an hard iron lock!
Blood vessels are fused to increase circulation and these conjoined or grafted veins and arteries make great painful lumps which have to be soaked daily.
2009, Alex Metcalfe, chapter 10, in The Muslims of Medieval Italy, Edinburgh University Press, page 196:
These 'signatures' (in Arabic ‘alāmāt; singular, ‘alāma) typically consisted of a phrase of up to half a dozen conjoined words written as a monogram in which the reed pen usually maintained contact with the parchment throughout.
Joined or bound together; united (in a relationship).
O my lord / The glory of whose new state is hidden from us, / Pray for us of your charity; now in the sight of God /Conjoined with all the saints and martyrs gone before you, / Remember us.
But as representatives of a loosely conjoined nation split in a hundred ways by personal, tribal, religious and economic rivalries and jealousies, no two of them went to the conference agreed on what independence should mean.
I have seen another woman who, from taste and necessity conjoined, has gone into practical affairs, carries on a mechanical business, partly works at it herself, […]
Usage notes
Conjoint is often used, but conjoined is the preferred usage.