Examples abound: historic – historical / electric – electrical / economic – economical…
Although they are similar, and sometimes used interchangeably, they may cause some confusion.
HISTORIC – REMARKABLE
HISTORICAL – RELATED TO THE PAST
ELECTRIC – THAT USES ELECTRICITY
ELECTRICAL – RELATED TO ELECTRICITY
ECONOMIC – RELATED TO THE ECONOMY (OF A COUNTRY, FOR EXAMPLE)
ECONOMICAL – THAT DOES NOT WASTE.
Curiously, the adverbs for the aforesaid pairs of words are the same: HISTORICALLY, ELECTRICALLY and ECONOMICALLY.