In American English, it’s an herb since the “h” is silent. In Britain, by contrast, the “h” is typically sounded, so they say “a herb”.

In American English, it’s an herb since the “h” is silent. In Britain, by contrast, the “h” is typically sounded, so they say “a herb”. Remember, the rule for using “a” or “an” is based on pronunciation, not spelling.

The poisoning was caused by an herb. (American English)

The poisoning was caused by a herb. (British English)

Another example:

You may need to take an herb for ten days. (American English)

You may need to take a herb for ten days. (British English)

Follow the same convention with the word herbal.

This is an herbal tea that comes from China. (American English)

This is a herbal tea that comes from China. (British English)

In general, other derived forms such as herbicide, herbaceous, herbivore, or herbivorous are more frequently pronounced with the consonant “h”. In American English, however, both options are acceptable and often used.

A/an herbicide is a product used to kill pests.

A partial list of words that also begin with a silent “h”, and therefore take the indefinite article “an”:

• an heir
• an heiress
• an heirloom
• an herbal (American English)
• an honest
• an honor
• an honorable
• an honorarium
• an honorary
• an hour
• an hourly
• an hourglass