This puzzle is based off the What is a Word™ and What is a Phrase™ series started by JLee and their spin-off What is a Number™ series.
If a word conforms to a certain rule, I call it a Complete Word™. Use the following examples to find the rule:
$$ % set Title text. (spaces around the text ARE important; do not remove.) % increase Pad value only if your entries are longer than the title bar. % \def\Pad{\P{0.0}} \def\Title{\textbf{ Complete }} % \def\S#1#2{\Space{#1}{20px}{#2px}}\def\P#1{\V{#1em}}\ \def\V#1{\S{#1}{9}} \def\T{\Title\textbf{Words }^™\Pad}\def\NT{\Pad\textbf{Not}\T\ }\displaystyle \smash{\lower{29px}\bbox[yellow]{\phantom{\rlap{rubio.2017.02.04}\S{6px}{0} \begin{array}{cc}\Pad\T&\NT\\\end{array}}}}\atop\def\V#1{\S{#1}{5}} \begin{array}{|c|c|}\hline\Pad\T&\NT\\\hline % \text{BEN}&\text{BILL}\\ \hline \text{BEAT}&\text{SLAP}\\ \hline \text{GEEK}&\text{NERD}\\ \hline \text{ABBEY}&\text{CHURCH}\\ \hline \text{ACHING}&\text{TIRING}\\ \hline \text{BALDING}&\text{RECEDING}\\ \hline \text{ABDICATING}&\text{RENOUNCING}\\ \hline \end{array}$$
CSV version:
Ben,Bill
Beat,Slap
Geek,Nerd
Abbey,Church
Aching,Tiring
Balding,Receding
Abdicating,Renouncing
These aren't the only Complete Words™, there are others that exist.
As a bonus, (when it's possible to do so) I will award a bounty to the person that finds the longest Complete Word. This must be a real word (in English). The bounty will be awarded 24 hours after the accepted answer.
If I'm not allowed to do the above, please tell me to edit.
Edit: Correct answer has been identified and accepted at 22:45 GMT 7th March 2018.