The term 'Ruler of Thumb' is a phrase that has been used to describe the idea of using one's own judgment or experience as a guide. The two crossword solutions for this term are 'EBERT' (5 letters) and 'ROGEREBERT' (10 letters). EBERT is a surname derived from the Germanic name Eberhard, meaning 'strong as a boar'. RogerEbert was the name of the late American film critic, Roger EBERT, who was known for his use of thumb ratings to rate films.