Thymine is found in DNA, not in RNA. In the structure of DNA, thymine pairs with adenine, forming one of the crucial base pairs that help maintain the double-helix structure of DNA. However, in RNA, thymine is replaced by uracil. This replacement does not affect the overall function of RNA, but it is important to note the distinction between the two types of nucleic acids.
To summarize, thymine is a nitrogenous base specific to DNA, while RNA uses uracil in its place.