I came across this question and thought I would clarify that the lists() method of a eloquent builder object was depreciated in Laravel 5.2 and replaced with pluck().
// <= Laravel 5.1
Word_relation::where('word_one', $word_id)->lists('word_one')->toArray();
// >= Laravel 5.2
Word_relation::where('word_one', $word_id)->pluck('word_one')->toArray();
These methods can also be called on a Collection for example
// <= Laravel 5.1
$collection = Word_relation::where('word_one', $word_id)->get();
$array = $collection->lists('word_one');
// >= Laravel 5.2
$collection = Word_relation::where('word_one', $word_id)->get();
$array = $collection->pluck('word_one');