suàn

Re: suàn: I'm definitely not an expert, but I think those two different uses of suàn are internally consistent. Suàn means literally to calculate or tally. So in the "plan" sense it is calculating that makes the planning. It can be used as a request to ask for the bill in a restaurant, literally tally the cost of the dishes. In the case of "suànle", the translation "forget it" doesn't imply a literal translation of "to forget it". Rather, it is trying to convey "forget it" in the English colloquial sense, which is " It's over, I don't want to talk about it any more". Which would imply "consider the argument/conversation over, case closed." Or, the points for and against, consider tallied, the arguments done (even though I don't care about the presumed verdict or your opinion) and forgotton, I don't care. It's done. Just forget it. That's how I understand suàn in this context.

P.S. Please note I'm speaking not as an expert, but as someone trying to understand the different shades of the word without requiring myself to consider completely different meanings or etymologies. Perhaps someone from the team can advise? However as a non-expert I think I'm qualified to express my delight at a particularly exquisite pictographic representation of suàn in a language bursting rich with numerous lovely examples. 算 shows two hands at the bottom working on an abacus, made of bamboo, as indicated by the bamboo radical at the top. Lovely.