Strong Interaction

Yukawa deduced there had to be a short-range force like that of the weak interaction, one that could be felt only within the nucleus. This force would have to be much stronger than the weak interaction and indeed much stronger than the electromagnetic interaction in order to overcome proton repulsion, hence "strong".
 Hideki Yukawa Japan 1935 Strong Interaction

Yukawa deduced there had to be a short-range force like that of the weak interaction, one that could be felt only within the nucleus. This force would have to be much stronger than the weak interaction and indeed much stronger than the electromagnetic interaction in order to overcome proton repulsion, hence "strong".