You can substitute words which are synonyms. They can be used in place of each other.
substitute teacher and submarine
antonyms
Articles, items, or stuff. (Note that "stuff" is considered slang, but many people do use it instead of "things"-- for example: I have a lot of stuff in my basement.)
candid truthful trustworthy
Read the context to find possible words; use the word length and shape to find possible letters. If that fails, wing it and substitute a new word.
You can use parsley as a substitute for cilantro in this recipe.
nothing, there is no substitute
You can use oregano or thyme as a substitute for marjoram in soup.
You can use oregano or thyme as a substitute for marjoram in recipes.
You can use a combination of cinnamon and nutmeg as a substitute for cardamom in your recipe.
Another synonym is intermittent. You could also use the words random irregular occasional
You can use butter or margarine as a substitute for Crisco shortening in this recipe.
You can use a cooling rack or a bed of vegetables as a substitute for a roasting rack.
You can use lemon juice or tamarind paste as a substitute for amchoor in your recipe.
You can use baking powder as a substitute for bicarbonate of soda in the recipe.
You can use cornstarch or arrowroot powder as a substitute for flour in gravy to thicken it.
You can use unsalted butter as a substitute for salted butter in the recipe.