actinic keratosis (MONDO_0005173, a Monarch Disease Ontology term) is a precancerous lesion of the skin composed of atypical keratinocytes. It is characterized by the presence of thick, scaly patches of skin. Several histologic variants have been described, including atrophic, acantholytic, and hyperkeratotic variants. Also known as: SK - solar keratosis, actinic (solar) keratosis, actinic keratosis (disease), solar keratosis.