Adjective
unrigorous (comparative more unrigorous, superlative most unrigorous)
Not rigorous.
There is nothing special or interesting about this, as it fits in with the more general trend of unrigorous ideas which are later made rigorous. Source: Internet
To observe that rigorous proof comes only after unrigorous conjecture, experimentation and speculation is true, but it is trivial and no-one would deny this. Source: Internet