Long vs. Longly — What's the Difference?

"Long" is primarily used as an adjective to describe something that extends for a significant distance or duration. For example, it can refer to a long journey or a long rope. On the other hand, "longly," though grammatically correct, is an archaic or literary adverb and is rarely used in modern English; it means 'for a long time' or 'at great length.'

In contemporary usage, "long" can modify nouns directly, as in phrases like "a long speech" or "a long road." Whereas "longly" would theoretically modify verbs, relating to the duration of an action, such as "he gazed longly," but in practice, this form is almost never seen today.

"Long" is versatile and can also appear as an adverb in certain contexts, particularly in the comparative or superlative form, like "longer" or "longest." Meanwhile, "longly" does not vary and remains a rare and stylistically specific choice, primarily appearing in historical or poetic texts.

The use of "long" is widespread in both spoken and written English, applicable in everyday conversation, formal writing, and technical descriptions. In contrast, "longly" is generally considered outdated, and using it might confuse contemporary audiences or give a text an unintentionally old-fashioned tone.

Grammatically, "long" supports a variety of expressions, such as "as long as" (conditional) or "all night long" (duration). "Longly," if used, does not offer such flexibility and is limited to its singular, seldom-used adverbial form.