Yes, inside is a Scrabble word!

Adverb

1. Within a building

2. On the inside

3. With respect to private feelings

4. In reality

Adjective

1. Relating to or being on the side closer to the center or within a defined space

2. Being or applying to the inside of a building

3. Confined to an exclusive group

4. Away from the outer edge

Noun

1. The region that is inside of something

2. The inner or enclosed surface of something