According to the Wikipedia article Twelve Nidānas, the Pali word for Attachment is Upādāna (and that Wikpedia section has an unreferenced description of it).
That also links to a whole Wikipedia article on the subject, Upādāna, which says,
Upādāna and taṇhā are seen as the two primary causes of suffering. The cessation of clinging leads to Nirvana.
That statement in that article does have a lot of references.
However, I note that the Third Noble Truth in the Dhammacakkappavattana Sutta says "desire" and not "attachment". This commentary says,
Furthermore, bhikkhus, this is the dukkha·nirodha ariya·sacca: the complete virāga, nirodha, abandoning, forsaking, emancipation and freedom from that very taṇhā.
... where Taṇhā means thirst or desire.
Clearly, though, desire and attachment are related.
The Upadana Sutta starts with,
Dwelling at Savatthi. There the Blessed One said to the monks:
"In one who keeps focusing on the allure of clingable phenomena (or: phenomena that offer sustenance = the five aggregates), craving develops. From craving as a requisite condition comes clinging/sustenance.
I think that those two quoted sentences are saying:
- If you focus on what's alluring about something that you are or can become attached to, then you'll desire that thing
- If you desire something then you become attached to (cling to) it
In summary I think that if desire is like thirst then attachment is the object of that desire. For example you might think,
I am thirsty therefore I would like some water
... in which case you have attached to water as the object of your desire.
Similarly if you desire a person, then the desire is desire and the person (or more specifically your idea or 'reification' of that person) is the object of your desire and thus the focus of your attachment.
I suspect that attachment is also related to ego or sense of self, if you become attached to something then you identify with it, you think, "I desire this, I am the person who feels desire for this", etc.
I say that because the Upadana Sutta above said that the "clingable phenomena" are the five aggregates; and the Anatta-lakkhana Sutta also talks about the five aggregates including the famous saying,
Any [of each of the five aggregates] must, with right understanding how it is, be regarded thus: 'This is not mine, this is not I, this is not my self
Wikipedia's Manifestations of clinging says,
To distinguish craving from clinging, Buddhaghosa uses the following metaphor:
"Craving is the aspiring to an object that one has not yet reached, like a thief's stretching out his hand in the dark; clinging is the grasping of an object that one has reached, like the thief's grasping his objective.... [T]hey are the roots of the suffering due to seeking and guarding."
Although I may be wrong (perhaps I have misunderstood what 'attachment means), but I might not quite agree with that metaphor: because I think it's possible to be attached even to an object that you don't or cannot grasp.
For example if you were to think, "If only I had that person, or, if only I had that thing, then I'd be happy", then I think that's not only generalized desire (for an object) but also specific attachment (to a specific object): even when and even though you don't or cannot have/grasp/own/reach that object.
Presumably though you can be said to "have it" in the sense that "you have the idea of it".