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.