'Inflammable' has always meant 'tends to catch fire easily'; but, because the prefix 'in-' often means 'not' (as in 'ineffective')and for that reason 'inflammable' might be misinterpreted, 'flammable' ...
The words flammable and inflammable are often misinterpreted as opposites. As a matter of fact, flammable and inflammable mean exactly the same — capable of burning. Eg:Petrol is highly flammable.