What is the difference between 'abd and 'abid?

The words "abd" (servant) and "abid" (worshipper) refer to a single meaning, and an increase in the letters of a word indicates an increase in its meaning. Thus, an "abid" is one who has gone to great lengths in asceticism and worship of Allah the Almighty, while "abd" is generally used for one who has fulfilled the obligations of servitude without perfecting it. Therefore, every "abid" is an "abd," but not every "abd" is an "abid." The word "abd" may also be used for one who has gone to great lengths in asceticism and worship, as in the verse: "And remember Our servant (abdana) Dawud."