Tosh/tɑːʃ/ Definition 1 of 2Pro Tip 1/3British Slang Used mostly in the UK, so may not be well understood internationally. My American friend didn't understand when I called his idea tosh. Pro Tip 2/3Mild Disapproval Tosh expresses disagreement without being too harsh; it's less offensive than 'lies'. That's complete tosh, but I see why you might think that. Pro Tip 3/3Not for Formal Use Best used in casual conversation; avoid in formal or academic writing. In the meeting, he had to bite his tongue to not call the suggestions tosh.