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.