The definition of onerous is something hard to do, or troublesome.
An example of onerous is telling someone you betrayed them.
Troublesome or oppressive; burdensome.
Origin of onerous
Middle English from Old French onereusfrom Latin onerōsusfromonusoner-burden
American Heritage Dictionary of the English Language, 5th Edition
From Latinonerosus (“burdensome"), from onus (“load").
Onerous Sentence Examples
His duties were thus rendered exceedingly onerous, and his labour became excessive.
In 1584, however, the city had to surrender on onerous terms to the prince of Parma.
Accordingly, though France made every attempt to induce Turkey to adopt her side, the young Stratford Canning succeeded in causing the resumption of the peace negotiations at Bucharest, broken off through Russia's terms being considered too onerous, and followed by the capture of Izmail and Bender.
The conditions, however, upon which Wallenstein consented to come to the emperors aid were remarkably onerous, but Ferdinand had perforce to assent to them.
The high road from Kabul to Kandahar passes this way (another reason for supposing the Tarnak to be Arachotus), and the people live off the road to avoid the onerous duties of hospitality.