What part of speech is “science”

science is a noun referring to a field of study that uses empirical evidence to observe, measure, and explain the natural world. It can refer to the body of knowledge of such study, investigate topics related to it or the academic and professional discipline which studies it. It is usually used with the definite article, i.e. 'the science of physics' or 'the science of global warming.'

1. That student has an impressive grasp of science.

2. Global warming is a subject for ongoing science investigations.

3. The science of aeronautics is essential for any aerospace engineering program.

when talking about a specific set of sciences or topics related to science, always use the definite article 'the' before 'science'; when speaking generally, the 'the' can be omitted.