Highly flammable could also be written as 'highly inflammable'. The words 'highly flammable' refer to state of a substance. Highly acts as an adverb and describes the adjective flammable in detail. Highly could mean more, most, or very or largely. The word flammable could mean burnable. When something catches fire easily, it is said to be flammable or inflammable. Thus, the substance is dangerous or hazardous, ignitable or combustible, burnable or incendiary, risky or unsafe.
For example: highly flammable liquid. Here it describes a liquid that has a tendency to catch fire easily as compared to other liquids. Otherwise for substances that burn, there the use of highly is redundant. Another example: the issue was highly flammable: here the highly flammable indicates the seriousness of the issue and not its combustibility. This issue could lead to fights and tends to give rise to more differences.
For example: highly flammable liquid. Here it describes a liquid that has a tendency to catch fire easily as compared to other liquids. Otherwise for substances that burn, there the use of highly is redundant. Another example: the issue was highly flammable: here the highly flammable indicates the seriousness of the issue and not its combustibility. This issue could lead to fights and tends to give rise to more differences.