Ajahn Thanissaro, for example, uses this dual meaning several times, most notably in Mind like Fire Unbound.
andUpādāna carries both of its meanings — clinging & sustenance — when applied to the mind. It refers on the one hand both to mental clinging & to the object clung to, and on the other to both the act of taking mental sustenance & the sustenance itself.
Similarly, Gombrich, in What the Buddha Thought, says that the Pali term has an abstract meaning of grasping, and a more concrete meaning of sustenance or fuel for a process. Missing this double meaning makes the metaphors about fire, extinguishing, cooling, etc., harder to understand.Once a fire has been provoked, it needs 'upādāna' — commonly translated as fuel — to continue burning. Upādāna has other meanings besides fuel, though — one is the nourishment that sustains the life & growth of a tree — and as we will see below, wind can also function as a fire's upādāna. Thus, 'sustenance' would seem to be a more precise translation for the term.
The P.E.D. linked on Sutta Central agrees:
The former meaning is easy to accept, in the sense of "taking up". upa-ādānaupādāna
taking as one’s own, laying hold of, grasping.
material support or cause, fuel; (it is often difficult to determine which meaning is intended; both reinforce each other: previous grasping produces fuel, which is itself then grasped).
But is there anywhere in the canon a clear use of the term as equivalent merely to "fuel" or "sustenance for a process"? How do we know from the context that upādāna has this second sense?