【Largely】 , 【greatly】 , 【mostly】 , 【chiefly】 , 【mainly】 , 【principally】 , 【generally】 are often interchanged, but they are capable of being used with explicitness even though they basically agree in meaning.
【Largely】 stresses quantity or extent; it usually connotes copiousness or abundance and often suggests an amount exceeding that of other ingredients, components, or constituents.
【Greatly】 carries a heightened suggestion of greatness in degree that differentiates it from 【largely】 .
【Mostly】 usually stresses numbers.
【Chiefly】 emphasizes the importance of one thing among other things; it may connote an outstanding or preeminent position or it may connote merely relative importance <the basket contained many fruits, but 【chiefly】 apples> <the battle was won 【chiefly】 by the aid of the air force>
【Mainly】 is often used interchangeably with 【chiefly】 , but not where preeminence is implied; rather it connotes greatest importance among a number of things, but not exclusive value <be sure to take along with you all that you will need, but 【mainly】 informal clothes> <the cause depends 【mainly】 on the validity of this act —John Marshall > <the Pickwickian Christmas did very little to stimulate consumption; it was 【mainly】 a gratuitous festivity —Huxley >
【Principally】 carries an idea of primary importance rather than outstanding or relative importance; the difference is not great between it and 【chiefly】 or 【mainly】 except when the idea of being first or primary is emphasized <they wholly mistake the nature of criticism, who think its business is 【principally】 to find fault —Dryden > <his support comes 【principally】 from the income of invested money> <the cash crops are 【principally】 wheat and rye>
【Generally】 stresses reference to the majority of persons, instances, or cases involved <the people, not universally, but 【generally】 , were animated by a true spirit of sacrifice —Froude > <the news was 【generally】 received with joy> <the land breezes here are 【generally】 hot and dry>
