Nonsensical, a.
Without sense; unmeaning; absurb; foolish; irrational; preposterous. -- Non*sen"si*cal*ly, adv. -- Non*sen"si*cal*ness, n.
Shades of meaning
Fernald has no entry of its own for nonsensical; he lists it under absurd.
Where he writes about it:
The ridiculous or the nonsensical is worthy only to be laughed at. — from absurd
The lunatic's claim to be a king is ridiculous; the Mother Goose rimes are nonsensical. — from absurd