onerosity

from The Century Dictionary.

• noun The fact of being onerous; specifically in Scots law, the fact that a deed, contract, note, or the like, has valid consideration. See onerous, 2.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun rare Onerousness.
• noun Scotland, law The legal state of affairs resulting from being done or given in return for receipt of something of value.