The term 'diligently work' can be broken down into four crossword solutions: PLY (3 letters), PORE (4 letters), PLIED (5 letters), and PLYING (6 letters). PLY is a verb meaning to work diligently, while PORE is a verb meaning to read or study something carefully. PLIED is the past tense of PLY, and PLYING is the present participle of PLY. Therefore, the four crossword solutions all refer to working diligently in some form.