frenillo
frenulum
freno
brake
+
-illo
diminutive suffix
Frenillo means frenulum and can be thought of as a small brake0 (freno0) with the diminutive suffix1 (-illo1) indicating its small size. A frenulum is indeed a small tissue that restrains or holds back an organ.
noun
- frenulumA small fold of tissue that connects or restricts the motion of a body partEl dentista examinó el frenillo de la lengua del paciente. // The dentist examined the patient's tongue frenulum.