in ‧ ter ‧ pen ‧ e ‧ trate /ˌɪntəˈpenətreɪt, ˌɪntəˈpenɪtreɪt $ -tər-/ BrE AmE verb [intransitive and transitive] formal
to spread through something or spread through each other
—interpenetration /ˌɪntəpenəˈtreɪʃ ə n, ˌɪntəpenɪˈtreɪʃ ə n $ -tər-/ noun [uncountable and countable]