Dictionary definitions often use plus signs when describing what words or phrases are made of. For example, the definition for たところで…ない in 大辞泉 says:
I think the basic pronunciation of the plus sign in math is たす. But this isn't math, and I'm curious if people would pronounce it differently in this context.
For example, If I were reading this definition aloud, could I also say に instead of たす? I have a feeling that might be appropriate, but I'm not sure.