That accords with the correct or accepted procedure, method, or rule; governed by a rule or rules; regular.
Mid 16th century; earliest use found in John Vaus (c1484–c1539), grammarian. From rule + -ful.
英汉双解词典包含464360条英汉词条，基本涵盖了全部常用单词的翻译及用法，是英语学习的有利工具。