Repulsive means so unpleasant that it drives you away. A repulsive smell, repulsive behaviour, frankly repulsive.
It is stronger than disgusting and describes something that actively pushes you back, which is what the word literally means. In physics, a repulsive force pushes apart, as against an attractive one, and that use is entirely neutral. Note repulse, which means to drive back and also to reject; repulsion, which covers both the feeling and the physics; and that repulsive and repellent are near-identical in strength.
1adjectiverepulsiveSo unpleasant it drives you away.
“The rotting fish in the bin gave off a repulsive smell.”
synonyms: revolting, repellent
2adjectivepushingPushing apart, of a force.
“Two north poles of a magnet produce a repulsive force when brought together.”
repulsive is a quality of driving away.
Latin repellere is re-, back, plus pellere, to drive — the same verb as propel, expel and compel. Something repulsive drives you back, which is a physical claim rather than a metaphor.
Latin
repulsus
Medieval Latin
repulsivus
Middle French
repulsif
English, today
repulsive
Middle French repulsif, from Medieval Latin repulsivus, from Latin repulsus. by surface analysis, repuls(e) + repulse + -ive. Compare typologically odpychający (< pchnąć), отта́лкивающий (< толкну́ть).
Etymology from Wiktionary, CC BY-SA