contrary to reason or common sense; utterly absurd or ridiculous.
feeling or expressing overwhelming happiness or joyful excitement.
having a full rounded shape
Preposterous - contrary to reason or common sense; utterly absurd or ridiculous.
When Sandy's stock broker called and suggested that he sell half his stocks because he felt the market was overvalued, Sandy thought the idea was preposterous - but it turned out that his stock broker was right.