"Think nothing of" means to consider something as unimportant, irrelevant, or insignificant. Some synonyms for this phrase include disregard, dismiss, ignore, overlook, minimize, and shrug off. When using these synonyms, the speaker intends to convey that the particular matter is being treated lightly or without due consideration, and that it is not worth much thought or attention. For example, "She dismissed the insulting comment, thinking nothing of it," or "He shrugged off the criticism, ignoring it completely." Using these synonyms can often help add variety to writing or speech, and accurately express the intended meaning.