Testicular is the describing word that goes with testicle: relating to the testicles. It is a medical word and you will nearly always meet it attached to another word rather than standing alone — testicular cancer above all, which is one of the most common cancers in younger men and one that is usually cured if it is found early. You also see testicular pain, testicular examination, a testicular lump. A doctor writes it; a patient normally says 'a pain in my testicle' instead. So think of it as the technical partner of the everyday noun, useful mainly for reading health information and for understanding a doctor.