Synonyms and related words :
always trot out, apply the mind, belabor, dig, drudge, dwell on, dwell upon, fag, grind, grub, hammer, hammer at, hammer away, harp on, insist upon, keep doggedly at, labor, moil, peg, peg away, plod, plug, plug along, plug at, plug away, pound away, puzzle, puzzle over, slog, slog away, stew over, think hard, thresh over, toil, travail, wade through, work away