“Inter-” and “intra-” are difficult to keep straight.
“Inter-” means between different groups. “Intra-” means within the same group. This will be more clear with examples.
Intermolecular forces are forces between different molecules. Intramolecular forces are forces within the same molecule.
Intercellular means between different cells. Intracellular means within the [same] cell.
Think of it like highways. Interstate highways are those highways that cross state lines (cross multiple states). Intrastate highways is a less common expression, but one can think of it as highways/roads that are only meaningful in the same state.
