adjective
an adjective describes a noun or pronoun, in this case 'infrequent' describes something that does not occur often
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Her visits to the museum were infrequent due to her busy work schedule.
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I don't see him very often, he's quite infrequent around here.
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She's a rare sight, very infrequent in these parts.
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His contributions to the project were infrequent, like a rare gem in a field of rocks.