Here's why:
* Phrase: It consists of two words working together to convey a single meaning.
* Adverb: It modifies a verb, adjective, or another adverb.
Examples:
* Verb Modification: "I will be at least 30 years old by next year." ("At least" modifies the verb "be")
* Adjective Modification: "It is at least a mile to the store." ("At least" modifies the adjective "mile")
* Adverb Modification: "I went to bed at least an hour earlier than usual." ("At least" modifies the adverb "earlier")
It's important to note that while "at least" acts as a single unit, it is not a single word.