1. Pertaining to something which is quite large or significant: The caretakers set up a substantial number of seats for the guests for the big farewell party at the office.
2. Concerning a sufficient and plentiful amount of food: Before going on the long hike up the mountain, Jack and Jill had a very substantial and wholesome breakfast at the hotel.
3. Regarding the excellent quality or condition of something: Janet wanted her house to be build solidly with substantial timber, and not with plywood.
4. Characterizing a fact with a firm basis; not imaginary: Sam and Susan had a substantial and happy relationship which was fundamental for living together for so many years!
5. Descriptive of something worthwhile or important: The politicians were thinking of making substantial reforms regarding the tax system.
6. Denoting wealth or importance: Because Grace had substantial funds in the bank, she was able to go on trips around the world every year!